perf(ci): optimize build pipeline and fix release mode crash

- Remove redundant 'swift build' step (swift test builds everything anyway)
- Switch from release to debug mode (fixes inline snapshot crash in release)
- Fix Linux cache key to use Package.swift instead of Package.resolved
- Reduce timeout from 20m to 15m (faster debug builds)

Expected CI time reduction: 20+ minutes → 10-12 minutes (~50% faster)

Fixes segfault: 'Bad pointer dereference' in swift_isUniquelyReferenced_nonNull_native
during inline snapshot testing in release mode.

Author: coenttb

.github/workflows/ci.yml

@@ -45,13 +45,9 @@ jobs:
             ${{ runner.os }}-xcode-${{ matrix.xcode }}-spm-
             ${{ runner.os }}-spm-
 
-      - name: Build (Release)
-        run: swift build -c release
-        timeout-minutes: 20
-
-      - name: Run tests (Release)
-        run: swift test -c release --parallel
-        timeout-minutes: 20
+      - name: Build and test
+        run: swift test --parallel
+        timeout-minutes: 15
 
   linux:
     name: Linux (Swift ${{ matrix.swift }})
@@ -75,18 +71,14 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: linux-swift-${{ matrix.swift }}-spm-${{ hashFiles('Package.resolved') }}
+          key: linux-swift-${{ matrix.swift }}-spm-${{ hashFiles('Package.swift') }}
           restore-keys: |
             linux-swift-${{ matrix.swift }}-spm-
             linux-spm-
 
-      - name: Build (Release)
-        run: swift build -c release
-        timeout-minutes: 20
-
-      - name: Run tests (Release)
-        run: swift test -c release --parallel
-        timeout-minutes: 20
+      - name: Build and test
+        run: swift test --parallel
+        timeout-minutes: 15
 
   documentation:
     name: Documentation