Add client sampling

[SecretiveShell]

This adds a sampling request handler parameter to the ClientSession Class.

Motivation and Context

This will allow for receiving sampling requests inside of python clients.

How Has This Been Tested?

This still needs extensive testing, but for now I have been testing using this example repo https://github.com/SecretiveShell/MCP-python-client-sampling-demo

Breaking Changes

None

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Currently this PR is failing, the example tests work but the response from the everything server is resp.content[0].text='LLM sampling result: [object Object]' I am opening this as a draft PR for the opportunity to get feedback and iterate on the implementation. This is now resolved

[SecretiveShell]

seems like the object Object issue is not related to this implementation modelcontextprotocol/servers#477

[dsp-ant]

I like the concept here. Do you mind pushing this over the finish line? Cleanup, Documentation and Tests?

[SecretiveShell]

Glad you feel that this is the correct way to go about implementing this, if there are no desired changes I am happy to start pushing forwards with docs/testing.

[SecretiveShell]

I've confirmed the functionality is working on my end. However, the testing is blocked by the issue with the sampling test tool in the everything server. Once that's fixed, I can add proper unit tests. Let me know if there are other changes needed in the meantime.

[SecretiveShell]

removing the assert statements verifying the sampling call-back signature will likely lead to client developers having to deal with really long tracebacks inside of sdk code, without good error messages. Is there any reason these were removed?

[SecretiveShell]

Superseded by #218