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/state.py

@@ -14,7 +14,7 @@ class State(object):
     def __init__(self):
         self.is_initialized = False
         self.exit_event = None
-        self.endpoints = []  # type: List[EndpointBase]
+        self.sockets = []  # type: List[SocketBase]
 
     def initialize(self):
         if self.is_initialized:
@@ -33,8 +33,8 @@ class State(object):
     def deinitialize(self):
         if not self.is_initialized: return
 
-        for endpoint in self.endpoints:
-            endpoint.close()
+        for socket in self.sockets:
+            socket.close()
 
         self.is_initialized = False