Make PortForwardResult implement Closeable and expose handler state

[Copilot]

PortForwardResult's underlying WebSocketStreamHandler remains open unless closed remotely, and methods like getInputStream() throw IllegalStateException when closed with no way to check state first.

Changes

• WebSocketStreamHandler: Add isClosed() method to expose closed state
• PortForwardResult: Implement Closeable, add isClosed() and close() methods

Aligns with existing Attach.AttachResult which already implements Closeable.

Usage

try (PortForwardResult result = forward.forward(pod, ports)) {
    if (!result.isClosed()) {
        InputStream is = result.getInputStream(8080);
        // ...
    }
}

Fixes #2911

Original prompt

---

This section details on the original issue you should resolve

<issue_title>PortForwardResult does not expose methods to close WebSocketStreamHandler nor expose is state</issue_title>
<issue_description>Describe the bug
PortForwardResult's underlying WebSocketStreamHandler will remain open unless the WebSocket is closed remotely. Furthermore, PortForwardResult's methods that return streams will throw an IllegalStateException if the handler is closed, but does not expose a way to check the handler state to avoid the exception.

This is related to #865 but more specific.

Client Version
16.0.0

Kubernetes Version
1.24.0

Java Version
Java 11

To Reproduce
Steps to reproduce the behavior:

1. Call PortForward.forward
2. Call getInputStream/getOutputStream on the result with try-with-resources pattern

Expected behavior

1. There is a way to check the state to avoid an IllegalStateExeption, e.g. exposing WebSocketStreamHandler.state via PortForwardResult.
2. There is a way to close the underlying WebSocketStreamHandle, e.g. having PortForwardResult implement AutoCloseable and closing the WebSocketStreamHandle on close.

Server (please complete the following information):

• OS: Linux (Debian Bookworm)
• Environment: KinD
• Cloud: None
  </issue_description>

Comments on the Issue (you are @copilot in this section)

@brendandburns We'd be happy to have a PR to extend support to cover this. @ /assign I don't know much about java, but i know C. I would like to give it a try. new to open source. Will try my best. @ @brendandburns I don't know much right now. How much time do I have to resolve this Issue? Asked this to get an idea about how much time i have to learn.

• Fixes PortForwardResult does not expose methods to close WebSocketStreamHandler nor expose is state #2423

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[brendandburns]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brendandburns, Copilot

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