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/receiver_base.py

@@ -0,0 +1,21 @@
+from abc import ABCMeta, abstractmethod
+
+from robot_interface.endpoints.endpoint_base import EndpointBase
+
+
+class ReceiverBase(EndpointBase, object):
+    """Associated with a ZeroMQ socket."""
+    __metaclass__ = ABCMeta
+
+    @abstractmethod
+    def handle_message(self, message):
+        """
+        Handle a message with the receiver.
+
+        :param message: The message to handle.
+        :type message: dict
+
+        :return: A response message.
+        :rtype: dict
+        """
+        return {"endpoint": "error", "data": "The requested receiver is not implemented."}