Fix test flakiness

[Evangelink]

Fix #7398

[Copilot]

Pull request overview

Addresses flakiness in the server-mode TCP startup/abort path (Issue #7398) by tightening cancellation handling around TCP connection establishment and by broadening the set of cancellation-adjacent exceptions treated as expected during shutdown/abort.

Changes:

• Adds a post-ConnectAsync cancellation check before calling TcpClient.GetStream() to avoid a race where the socket is closed by cancellation.
• Consolidates multiple cancellation-related catch blocks in ServerTestHost into a single filtered catch that also covers InvalidOperationException from GetStream().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/MessageHandlerFactory.cs	Adds a cancellation guard between successful connect and GetStream() to prevent “non-connected sockets” failures.
src/Platform/Microsoft.Testing.Platform/Hosts/ServerTestHost.cs	Expands/centralizes cancellation exception handling to treat additional timing-dependent socket exceptions as expected during abort.