Overhaul service lifecycle for Structured Concurrency (#130)

* Overhaul service lifecycle for Structured Concurrency

# Motivation
Since the release of Swift Concurrency the server ecosystem has adopted `async`/`await` in a lot of APIs making the user experience amazing. Another thing that Swift Concurrency introduced is Structured Concurrency which allows to create a task tree that with parent to child relations. Structured Concurrency has many benefits such as automatic cancellation and task local propagation.
The current state of this library predates the introduction of Swift Concurrency and is not inline anymore with how applications are structured that want to leverage Concurrency.

# Modification
This PR overhauls the implementation of service lifecycle completely. The reason for this is that the current implementation is very focused on how NIO based applications work before the introduction of Concurrency. Furthermore, Structured Concurrency is actually replacing part of the current functionality by providing new scoping mechanisms.
The overhauled implementation provides two primitive types. Anew `Service` protocol and a `ServiceRunner`. The former is providing a clear API which services have to conform to so that they can be run by the `ServiceRunner`.

An example usage of the types looks like this

```swift
actor FooService: Service {
    func run() async throws {}

    func shutdownGracefully() async throws {}
}
actor BarService: Service {
    func run() async throws {}

    func shutdownGracefully() async throws {}
}

let fooService = FooService()
let barService = BarService()

let runner = ServiceRunner(
    services: [fooService, barService],
   configuration: .init(),
   logger: logger
)

try await runner.run()
```

# Result
We now have a service lifecycle library that integrates nicely with Structured Concurrency. Its value add is that it solves to complex setup of the task group with the signal handling. Furthermore, it provides a currency type `Service` that can be passed to inject services.

* Remove `shutdownGracefully` method and switch to a handler based approach.

* Code review from George

* Add extensions to `TaskGroup` and `ThrowingTaskGroup`

* Remove long running property

* Documentation

* Fix tests

* Ensure ordering of shutdown

* Test

# Motivation

# Modification

# Result

* Introduce ServiceLifecycleTestKit

* Add AsyncCancelOngracefulShutdownSequence

* Tests and docs for graceful shutdown

# Motivation

# Modification

# Result

* Remove unsafe flags

* Add article for application authors

* Add correct licence and notice information for the things we copied from swift-nio

* Code review

* Remove @_unsafeInheritExectuor

* Code review

* Change log levels, rename to withGracefulShutdownHandler and support nested service runner graceful shutdown

* Add public `shutdownGracefully` method to the service runner

* Code review and expose new cancelOnGracefulShutdown method

* Extend graceful shutdown APIs and tolerate running outside of a `ServiceRunner`

* Rename to `ServiceGroup`

* Enable Swift 5.6 support

* Update soundess dockerfile

* Update Readme

* Make 5.6 build work

Author: FranzBusch

.spi.yml

@@ -1,4 +1,4 @@
 version: 1
 builder:
   configs:
-    - documentation_targets: [Lifecycle, LifecycleNIOCompat]
+    - documentation_targets: [ServiceLifecycle, UnixSignals]

.swiftformat

@@ -1,13 +1,26 @@
 # file options
 
---swiftversion 5.0
+--swiftversion 5.7
 --exclude .build
 
 # format options
 
 --self insert
 --patternlet inline
+--ranges nospace
 --stripunusedargs unnamed-only
 --ifdef no-indent
+--extensionacl on-declarations
+--disable typeSugar # https://github.com/nicklockwood/SwiftFormat/issues/636
+--disable andOperator
+--disable wrapMultilineStatementBraces
+--disable enumNamespaces
+--disable redundantExtensionACL
+--disable redundantReturn
+--disable preferKeyPath
+--disable sortedSwitchCases
+--disable hoistTry
+--disable hoistAwait
+--disable redundantOptionalBinding
 
 # rules

NOTICE.txt

@@ -0,0 +1,36 @@
+
+The ServiceLifecycle Project
+===========================
+
+Please visit the ServiceLifecycle web site for more information:
+
+* https://github.com/swift-server/swift-service-lifecycle
+
+Copyright 2019-2023 The ServiceLifecycle Project
+
+The ServiceLifecycle Project licenses this file to you under the Apache License,
+version 2.0 (the "License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at:
+
+https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+License for the specific language governing permissions and limitations
+under the License.
+
+Also, please refer to each LICENSE.txt file, which is located in
+the 'license' directory of the distribution file, for the license terms of the
+components that this product depends on.
+
+---
+
+This product contains derivations of the Lock and LockedValueBox implementations from SwiftNIO.
+
+* LICENSE (Apache License 2.0):
+* https://www.apache.org/licenses/LICENSE-2.0
+* HOMEPAGE:
+* https://github.com/apple/swift-nio
+
+---

Package.swift

@@ -4,31 +4,83 @@ import PackageDescription
 
 let package = Package(
     name: "swift-service-lifecycle",
+    platforms: [
+        .macOS(.v10_15),
+        .iOS(.v13),
+        .watchOS(.v6),
+        .tvOS(.v13),
+    ],
     products: [
-        .library(name: "Lifecycle", targets: ["Lifecycle"]),
-        .library(name: "LifecycleNIOCompat", targets: ["LifecycleNIOCompat"]),
+        .library(
+            name: "ServiceLifecycle",
+            targets: ["ServiceLifecycle"]
+        ),
+        .library(
+            name: "ServiceLifecycleTestKit",
+            targets: ["ServiceLifecycleTestKit"]
+        ),
+        .library(
+            name: "UnixSignals",
+            targets: ["UnixSignals"]
+        ),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-atomics.git", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-log.git", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-metrics.git", "1.0.0" ..< "3.0.0"),
-        .package(url: "https://github.com/swift-server/swift-backtrace.git", from: "1.1.1"),
-        .package(url: "https://github.com/apple/swift-nio.git", from: "2.0.0"), // used in tests
-        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
+        .package(
+            url: "https://github.com/apple/swift-log.git",
+            from: "1.5.2"
+        ),
+        .package(
+            url: "https://github.com/apple/swift-docc-plugin",
+            from: "1.0.0"
+        ),
+        .package(
+            url: "https://github.com/apple/swift-async-algorithms",
+            from: "0.1.0"
+        ),
     ],
     targets: [
-        .target(name: "Lifecycle", dependencies: [
-            .product(name: "Atomics", package: "swift-atomics"),
-            .product(name: "Logging", package: "swift-log"),
-            .product(name: "Metrics", package: "swift-metrics"),
-            .product(name: "Backtrace", package: "swift-backtrace"),
-        ]),
-
-        .target(name: "LifecycleNIOCompat", dependencies: [
-            "Lifecycle",
-            .product(name: "NIO", package: "swift-nio"),
-        ]),
-
-        .testTarget(name: "LifecycleTests", dependencies: ["Lifecycle", "LifecycleNIOCompat"]),
+        .target(
+            name: "ServiceLifecycle",
+            dependencies: [
+                .product(
+                    name: "Logging",
+                    package: "swift-log"
+                ),
+                .product(
+                    name: "AsyncAlgorithms",
+                    package: "swift-async-algorithms"
+                ),
+                .target(name: "UnixSignals"),
+                .target(name: "ConcurrencyHelpers"),
+            ]
+        ),
+        .target(
+            name: "ServiceLifecycleTestKit",
+            dependencies: [
+                .target(name: "ServiceLifecycle"),
+            ]
+        ),
+        .target(
+            name: "UnixSignals",
+            dependencies: [
+                .target(name: "ConcurrencyHelpers"),
+            ]
+        ),
+        .target(
+            name: "ConcurrencyHelpers"
+        ),
+        .testTarget(
+            name: "ServiceLifecycleTests",
+            dependencies: [
+                .target(name: "ServiceLifecycle"),
+                .target(name: "ServiceLifecycleTestKit"),
+            ]
+        ),
+        .testTarget(
+            name: "UnixSignalsTests",
+            dependencies: [
+                .target(name: "UnixSignals"),
+            ]
+        ),
     ]
 )