On Windows, StdioClientTransport calls taskkill and triggers visible cmd windows

[JesseCol]

Describe the bug
When a StdioClientTransport shuts down, and the server-side process is still alive, MCP calls taskkill here.

04 ModelContextProtocol!ModelContextProtocol.Utils.ProcessHelper.RunProcessAndWaitForExit
05 ModelContextProtocol!ModelContextProtocol.Utils.ProcessHelper.KillTree
06 ModelContextProtocol!ModelContextProtocol.Protocol.Transport.StdioClientTransport.DisposeProcess
07 ModelContextProtocol!ModelContextProtocol.Protocol.Transport.StdioClientSessionTransport.CleanupAsync

When it does this, it triggers a visible cmd window on the user's machine.

I believe we can fix this by setting ProcessStartInfo.CreateNoWindow = true.

To Reproduce
I believe you just need to use STDIO transport, and close it on the client side.

Expected behavior
I expect taskkill to run without popping up any windows.