Send DELETE request when closing a Streamable HTTP session on the client

[halter73]

This updates StreamableHttpClientSessionTransport.DisposeAsyncto send a delete request.

5. Clients that no longer need a particular session (e.g., because the user is leaving the client application) SHOULD send an HTTP DELETE to the MCP endpoint with the Mcp-Session-Id header, to explicitly terminate the session.

• The server MAY respond to this request with HTTP 405 Method Not Allowed, indicating that the server does not allow clients to terminate sessions.

https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http

[halter73]

I updated this PR to now log any exceptions that might be thrown while sending the delete request.

I also included a fix for #512 so we don't have to wait on the auth PR. I scoped the ODE fix down to the StreamableHttpClientSessionTransport for now, but I could move this down to TransportBase in a later PR if we like the approach.

And finally, I also included a workaround for the race in Kestrel I describe in dotnet/aspnetcore#62385 that was causing some of our tests to hang. Until Kestrel is fixed, Kestrel may still think that it's waiting on the client to close the connection during shutdown causing Kestrel to unnecessarily wait an extra 30 seconds when the race condition occurs, but at least the tests should finish.