MCPToolset Support MCP Sampling

[kevensen]

MCP Sampling allows for an MCP server to request completions from a client. The client (an agent in this case) maintains control over the models but the MCP server can request access to an LLM and improve it's own responses.

This is described in the MCP specification: https://modelcontextprotocol.io/specification/2025-06-18/client/sampling.

[hangfei]

Closing this and please use the main issue to track.