feat: pydantic models and inter-process messaging

Moved `InternalMessage` into schemas and created a `BeliefMessage`
model. Also added the ability for agents to communicate via ZMQ to
agents on another process.

ref: N25B-316

test/unit/agents/bdi/test_belief_collector.py

@@ -84,4 +84,4 @@ async def test_send_beliefs_to_bdi(agent):
     sent: InternalMessage = agent.send.call_args.args[0]
     assert sent.to == settings.agent_settings.bdi_core_name
     assert sent.thread == "beliefs"
-    assert json.loads(sent.body) == beliefs
+    assert json.loads(sent.body)["beliefs"] == beliefs