fix: make VAD unit tests work with minimal dependencies

By mocking PyTorch and ZMQ and adding the Numpy dependency.

ref: N25B-213

test/unit/agents/test_vad_streaming.py

@@ -18,6 +18,9 @@ def audio_out_socket():
 
 @pytest.fixture
 def streaming(audio_in_socket, audio_out_socket):
+    import torch
+
+    torch.hub.load.return_value = (..., ...)  # Mock
     return Streaming(audio_in_socket, audio_out_socket)