refactor: rename EndpointBase to SocketBase

Because 'endpoint' is also used in the messages, the name 'socket' is more descriptive.

ref: N25B-168

src/robot_interface/endpoints/receiver_base.py

@@ -1,9 +1,9 @@
 from abc import ABCMeta, abstractmethod
 
-from robot_interface.endpoints.endpoint_base import EndpointBase
+from robot_interface.endpoints.socket_base import SocketBase
 
 
-class ReceiverBase(EndpointBase, object):
+class ReceiverBase(SocketBase, object):
     """Associated with a ZeroMQ socket."""
     __metaclass__ = ABCMeta