fix: make VAD unit tests work with minimal dependencies

By mocking PyTorch and ZMQ and adding the Numpy dependency.

ref: N25B-213

pyproject.toml

@@ -7,6 +7,7 @@ requires-python = ">=3.13"
 dependencies = [
     "fastapi[all]>=0.115.6",
     "mlx-whisper>=0.4.3 ; sys_platform == 'darwin'",
+    "numpy>=2.3.3",
     "openai-whisper>=20250625",
     "pyaudio>=0.2.14",
     "pydantic>=2.12.0",
@@ -33,6 +34,7 @@ integration-test = [
     "soundfile>=0.13.1",
 ]
 test = [
+    "numpy>=2.3.3",
     "pytest>=8.4.2",
     "pytest-asyncio>=1.2.0",
     "pytest-cov>=7.0.0",