Fix StdioServerTransport.DisposeAsync() hang: CancellableStdinStream missing Dispose override#1276

stephentoub merged 3 commits intomainmodelcontextprotocol/csharp-sdk:mainfrom

copilot/fix-flaky-test-stdio-server-transportmodelcontextprotocol/csharp-sdk:copilot/fix-flaky-test-stdio-server-transportCopy head branch name to clipboard