feat: pass session_id to session_cleanup_handler

[ntwerdochlib]

This pull request updates how session cleanup handlers are defined and invoked in the codebase. The main change is that session cleanup handlers now receive both the resource key and the session ID, allowing for more context-aware cleanup logic.

Session cleanup handler improvements:

• Updated the type definition of session_cleanup_handler in mcp_server.h so that handlers now take both a key and a session_id as arguments, instead of just the key.
• Modified the invocation of session cleanup handlers in server::close_session in mcp_server.cpp to pass both the key and session_id to each handler.