refactor: ZMQ context and proxy

Use ZMQ's global context instance and setup an XPUB/XSUB proxy intermediary to allow for easier multi-pubs.

close: N25B-217

src/control_backend/agents/vad_agent.py

@@ -9,7 +9,6 @@ from spade.behaviour import CyclicBehaviour
 
 from control_backend.agents.transcription import TranscriptionAgent
 from control_backend.core.config import settings
-from control_backend.core.zmq_context import context as zmq_context
 
 logger = logging.getLogger(__name__)
 
@@ -121,7 +120,7 @@ class VADAgent(Agent):
         return await super().stop()
 
     def _connect_audio_in_socket(self):
-        self.audio_in_socket = zmq_context.socket(zmq.SUB)
+        self.audio_in_socket = azmq.Context.instance().socket(zmq.SUB)
         self.audio_in_socket.setsockopt_string(zmq.SUBSCRIBE, "")
         if self.audio_in_bind:
             self.audio_in_socket.bind(self.audio_in_address)
@@ -132,7 +131,7 @@ class VADAgent(Agent):
     def _connect_audio_out_socket(self) -> int | None:
         """Returns the port bound, or None if binding failed."""
         try:
-            self.audio_out_socket = zmq_context.socket(zmq.PUB)
+            self.audio_out_socket = azmq.Context.instance().socket(zmq.PUB)
             return self.audio_out_socket.bind_to_random_port("tcp://*", max_tries=100)
         except zmq.ZMQBindError:
             logger.error("Failed to bind an audio output socket after 100 tries.")