Adds RPC endpoints and updates RPC response and error handling (#746)

* Fix rpc endpoints
Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

* Remove commented code
Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

* remove duplicate code in session registry

Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

* Linting fixes
Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

* Fix tests
Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

---------

Signed-off-by: Madhav Kandukuri <madhav165@gmail.com>

Author: madhav165

mcpgateway/cache/session_registry.py

@@ -1277,6 +1277,7 @@ async def generate_response(self, message: Dict[str, Any], transport: SSETranspo
             >>> # Response: {}
         """
         result = {}
+
         if "method" in message and "id" in message:
             try:
                 method = message["method"]