feat: add message_type to MCPMessage trait

[hashemix]

📌 Summary

• Added message_type() method to the MCPMessage Trait that returns a MessageTypes enum.
  Implemented for ClientMessage and ServerMessage enums
• Moved the request_id() method of the MCPMessage trait into a super trait (RPCMessage) , so MCPMessage could be also implemented for types that does not necessarily have a requestId or jsonrpc version.

Example:

fn print_message_type( message: ClientMessage ){
    if message.is_request() {
        println!("This message is a Request!");
    }
}