feat: DelaySum beamform plus hop process latency

Keep C920 stereo through SpeechBrain GCC-PHAT Delay-and-Sum, then
MetricGAN, and publish mono to LiveKit. Record last_dt_ms and log
process_ms/capture_ms every 50 hops for the latency plan.

tests/test_audio_cleanup.py

@@ -8,7 +8,7 @@ from audio_cleanup import AudioCleaner
 
 def test_enhance_batch_without_lengths_typeerror():
     c = AudioCleaner(mode="force")
-    assert c.backend == "model"
+    assert "model" in c.backend
     import torch
 
     w = torch.zeros(1, 8000)
@@ -17,7 +17,7 @@ def test_enhance_batch_without_lengths_typeerror():
 
 
 def test_process_uses_relative_lengths_one():
-    src = inspect.getsource(AudioCleaner.process)
+    src = inspect.getsource(AudioCleaner._process_inner)
     assert "tensor([1.0])" in src
 
 
@@ -48,3 +48,33 @@ def test_overlap_runs_model_after_enough_context():
         out = c.process(pcm)
         assert out.shape == (hop,)
         assert out.dtype == np.int16
+
+
+def test_beamform_loads_delaysum_module():
+    c = AudioCleaner(mode="off", beamform="force")
+    assert c._beamformer is not None
+    assert type(c._beamformer).__name__ == "DelaySum_Beamformer"
+    assert "beamform" in c.backend
+
+
+def test_process_records_last_dt_ms():
+    c = AudioCleaner(mode="off", beamform="off")
+    hop = 3200
+    pcm = (np.random.randn(hop) * 500).astype(np.int16)
+    c.process(pcm)
+    assert c.last_dt_ms >= 0.0
+
+
+def test_stereo_beamform_then_model_preserves_hop():
+    c = AudioCleaner(
+        mode="force", beamform="force", chunk_s=0.5, hop_s=0.25)
+    assert c.backend == "model+beamform"
+    hop = 4000
+    t = np.arange(hop)
+    ch0 = (np.sin(2 * np.pi * 440 * t / 16000) * 8000).astype(np.int16)
+    ch1 = np.roll(ch0, 3)
+    stereo = np.stack([ch0, ch1], axis=1)
+    for _ in range(4):
+        out = c.process(stereo)
+        assert out.dtype == np.int16
+        assert out.shape == (hop,)