Feature/617 async call tools

[davemssavage]

Work in progress towards Async Call Tools support as per modelcontextprotocol/modelcontextprotocol#617

Motivation and Context

To see if the protocol as defined in modelcontextprotocol/modelcontextprotocol#617 is implementable in practice, if so provide a reference implementation for others to follow

How Has This Been Tested?

Unit testing only at this stage

Breaking Changes

None planned, goal is to make this backwards compatible and opt-in

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

This patch is shared for discussion at this stage, it will be marked as draft. As noted in RequestCache class there are several TODOs of varying degrees of severity that need resolving before it should be considered for merge

[maxisbey]

Closing as the underlying spec PR (modelcontextprotocol/modelcontextprotocol#617) was closed.

_{AI Disclaimer}