Implement StreamableHTTP transport

Co-authored-by: Topher Bullock <topher.bullock@shopify.com>

lib/mcp/transport.rb

@@ -2,32 +2,57 @@
 
 module MCP
   class Transport
+    class << self
+      def register(name, transport_class)
+        @transports ||= {}
+        @transports[name] = transport_class
+      end
+
+      def get(name)
+        raise "Transport #{name} not found" unless @transports
+
+        @transports.fetch(name) { raise "Transport #{name} not found" }
+      end
+    end
+
+    # Initialize the transport with the server instance
     def initialize(server)
       @server = server
     end
 
+    # Send a response to the client
     def send_response(response)
       raise NotImplementedError, "Subclasses must implement send_response"
     end
 
+    # Open the transport connection
     def open
       raise NotImplementedError, "Subclasses must implement open"
     end
 
+    # Close the transport connection
     def close
       raise NotImplementedError, "Subclasses must implement close"
     end
 
-    private
+    # Handle a JSON request
+    # Returns a response that should be sent back to the client
+    def handle_json_request(request)
+      response = @server.handle_json(request)
+      send_response(response) if response
+    end
 
+    # Handle an incoming request
+    # Returns a response that should be sent back to the client
     def handle_request(request)
       response = @server.handle(request)
       send_response(response) if response
     end
 
-    def handle_json_request(request)
-      response = @server.handle_json(request)
-      send_response(response) if response
+    # Send a notification to the client
+    # Returns true if the notification was sent successfully
+    def send_notification(method, params = nil)
+      raise NotImplementedError, "Subclasses must implement send_notification"
     end
   end
 end