InjectedState in MCP tools

[streamnsight]

usage:
On the MCP server side, specify the key to map to the state with annotations:

@mcp.tool(annotations={"injected_state": "state"}) 
def tool(a: int = 0, b: Union[str, None] = None, state):
   pass

On the client side, it is handled automatically by the added code.

Caveat:

• trying to parse most types (base type, List, Unions, Literal, Optional) and default values, but probably not complete.
• no implementation for the converter from langchain tool to mcp tool at the moment

[streamnsight]

@eyurtsev for review.
Thanks