Bound ManagedSession reconnect cleanup

[Copilot]

Description

Reconnect integration cleanup could wait indefinitely on a dead transport, allowing a single stalled test to terminate the Sessions test host.

• Bounded test cleanup

  • Uses an independent 30-second cancellation token for CloseAsync.
  • Bounds DisposeAsync with a separate 30-second timeout.

• Non-blocking product disposal

  • Session.DisposeAsync sends CloseSession immediately without awaiting its response.
  • ManagedSession.DisposeAsync delegates inner-session disposal to this path.

Task closeSessionTask = base.CloseSessionAsync(
    null,
    DeleteSubscriptionsOnClose,
    default).AsTask();
_ = ObserveCloseSessionAsync(closeSessionTask);

• Regression coverage
  • Verifies disposal completes after dispatching CloseSession when the response never arrives.

Related Issues

Checklist

• I have signed the CLA and read the CONTRIBUTING doc.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added all necessary documentation.
• I have verified that my changes do not introduce (new) build or analyzer warnings.
• I ran all tests locally using the UA.slnx solution against at least .net framework and .net 10, and all passed.
• I fixed all failing and flaky tests in the CI pipelines and all CodeQL warnings.
• I have addressed all PR feedback received.

• Fixes Flaky CI hang: unbounded ManagedSession reconnect-test cleanup can crash the whole Sessions test host #4273

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