Implement SEP-2260 Require Server requests to be associated with a Client request

[guglielmo-san]

This issue tracks implementation of modelcontextprotocol/modelcontextprotocol#2260

[guglielmo-san]

The request in this SEP to associate the ServerRequests with ClientRequests overlaps with the SEP-2322, which entirely deprecate ServerRequests in favor of a unified InputRequest.