Add tests to verify McpClient.DisposeAsync doesn't hang

[halter73]

Add more tests for #1250.

[halter73]

@copilot Can you update this PR to use Task.WaitAsync instead of combining Task.WhenAny with Task.Delay?

[Copilot]

@halter73 I've opened a new pull request, #1253, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

Pull request overview

Adds regression coverage for issue #1250 to ensure McpClient.DisposeAsync() completes when HttpClientTransportOptions.OwnsSession=false in Streamable HTTP mode, including scenarios with an active GET/SSE stream and unsolicited server notifications.

Changes:

• Added a new conformance test that reproduces an indefinitely-open GET event stream and asserts disposal completes within a bounded time.
• Added two MapMcp integration tests asserting DisposeAsync does not hang with OwnsSession=false, including after an unsolicited notification is sent.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
tests/ModelContextProtocol.AspNetCore.Tests/StreamableHttpClientConformanceTests.cs	Adds a regression test simulating an active GET/SSE stream to verify client disposal completes when the client doesn’t own the session.
tests/ModelContextProtocol.AspNetCore.Tests/MapMcpStreamableHttpTests.cs	Adds integration tests for MapMcp Streamable HTTP verifying disposal doesn’t hang (with/without unsolicited notifications).