feat: implement transcriber agent

Uses speech fragments of the VAD agent, emits transcribed text over SPADE's default communication channel to no recipient for now.

ref: N25B-209

src/control_backend/agents/transcription/transcription_agent.py

@@ -0,0 +1,69 @@
+import asyncio
+import logging
+
+import numpy as np
+import zmq
+import zmq.asyncio as azmq
+from spade.agent import Agent
+from spade.behaviour import CyclicBehaviour
+from spade.message import Message
+
+from control_backend.agents.transcription.speech_recognizer import SpeechRecognizer
+from control_backend.core.config import settings
+from control_backend.core.zmq_context import context as zmq_context
+
+logger = logging.getLogger(__name__)
+
+
+class TranscriptionAgent(Agent):
+    """
+    An agent which listens to audio fragments with voice, transcribes them, and sends the
+    transcription to other agents.
+    """
+
+    def __init__(self, audio_in_address: str):
+        jid = settings.agent_settings.transcription_agent_name + "@" + settings.agent_settings.host
+        super().__init__(jid, settings.agent_settings.transcription_agent_name)
+
+        self.audio_in_address = audio_in_address
+        self.audio_in_socket: azmq.Socket | None = None
+
+    class Transcribing(CyclicBehaviour):
+        def __init__(self, audio_in_socket: azmq.Socket):
+            super().__init__()
+            self.audio_in_socket = audio_in_socket
+            self.speech_recognizer = SpeechRecognizer.best_type()
+            self._concurrency = asyncio.Semaphore(3)
+
+        async def _transcribe(self, audio: np.ndarray) -> str:
+            async with self._concurrency:
+                return await asyncio.to_thread(self.speech_recognizer.recognize_speech, audio)
+
+        async def run(self) -> None:
+            audio = await self.audio_in_socket.recv()
+            audio = np.frombuffer(audio, dtype=np.float32)
+            speech = await self._transcribe(audio)
+            logger.info("Transcribed speech: %s", speech)
+
+            message = Message(body=speech)
+            await self.send(message)
+
+    async def stop(self):
+        self.audio_in_socket.close()
+        self.audio_in_socket = None
+        return await super().stop()
+
+    def _connect_audio_in_socket(self):
+        self.audio_in_socket = zmq_context.socket(zmq.SUB)
+        self.audio_in_socket.setsockopt_string(zmq.SUBSCRIBE, "")
+        self.audio_in_socket.connect(self.audio_in_address)
+
+    async def setup(self):
+        logger.info("Setting up %s", self.jid)
+
+        self._connect_audio_in_socket()
+
+        transcribing = self.Transcribing(self.audio_in_socket)
+        self.add_behaviour(transcribing)
+
+        logger.info("Finished setting up %s", self.jid)