[JiyadAhammad]

Consumer cancellation of a ResponseType.stream response now cancels the adapter-response subscription, stops receive-timeout work, and awaits asynchronous source cleanup. Normal completion and later CancelTokens do not trigger duplicate closures.

Closes #2618

Motivation & Background

When a consumer stopped consuming a response stream early (e.g. response.data!.stream.first, take(), or manual subscription cancellation), handleResponseStream had no onCancel handler. As a result, the adapter socket remained connected and receiving bytes, the receive timer kept ticking, and late CancelToken invocations threw StateError.

Verification

Added 6 regression tests covering .first, direct cancellation, paused cancellation, asynchronous cleanup, and late tokens after normal completion/error. All 16 tests in dio/test/response/response_stream_test.dart pass on the Dart VM. Formatting and dart analyze are clean.

@cfug/dio-core This touches timeout/cancellation cleanup as called out in AGENTS.md §3. Public APIs and adapter signatures remain unchanged.

Implementation and tests developed with Antigravity assistance.

New Pull Request Checklist

• I have read the Documentation
• I have read the Agent Contribution Guidelines (required if any part of the change was produced with AI assistance)
• I have searched for a similar pull request in the project and found none
• I have updated this branch with the latest main branch to avoid conflicts (via merge from master or rebase)
• I have added the required tests to prove the fix/feature I'm adding
• I have updated the documentation (if necessary)
• I have run the tests without failures
• I have updated the CHANGELOG.md in the corresponding package

Additional context and info (if any)