feat: abstract base classes for endpoints

Introduces EndpointBase and ReceiverBase abstract base classes. Implements a ReceiverBase with the MainReceiver.

ref: N25B-168

src/robot_interface/endpoints/main_receiver.py

@@ -0,0 +1,48 @@
+import zmq
+
+from robot_interface.endpoints.receiver_base import ReceiverBase
+
+
+class MainReceiver(ReceiverBase):
+    def __init__(self, zmq_context, port=5555):
+        """
+        The main receiver endpoint, responsible for handling ping and negotiation requests.
+
+        :param zmq_context: The ZeroMQ context to use.
+        :type zmq_context: zmq.Context
+
+        :param port: The port to use.
+        :type port: int
+        """
+        super(MainReceiver, self).__init__("main")
+        self.create_socket(zmq_context, zmq.REP, port)
+
+    @staticmethod
+    def _handle_ping(message):
+        """A simple ping endpoint. Returns the provided data."""
+        return {"endpoint": "ping", "data": message.get("data")}
+
+    @staticmethod
+    def _handle_negotiation(message):
+        """
+        Handle a negotiation request. Will respond with ports that can be used to connect to the robot.
+
+        :param message: The negotiation request message.
+        :type message: dict
+
+        :return: A response dictionary with a 'ports' key containing a list of ports and their function.
+        :rtype: dict[str, list[dict]]
+        """
+        # TODO: .../error on all endpoints?
+        return {"endpoint": "negotiation/error", "data": "The requested endpoint is not implemented."}
+
+    def handle_message(self, message):
+        if "endpoint" not in message:
+            return {"endpoint": "error", "data": "No endpoint provided."}
+
+        if message["endpoint"] == "ping":
+            return self._handle_ping(message)
+        elif message["endpoint"] == "negotiation":
+            return self._handle_negotiation(message)
+
+        return {"endpoint": "error", "data": "The requested endpoint is not supported."}