fix: report gradient snr in db

tests/trainer/test_metric_util.py

@@ -0,0 +1,17 @@
+import pytest
+import torch
+
+from astrai.trainer.metric_util import GradSNRTracker
+
+
+def test_grad_snr_is_reported_in_decibels():
+    model = torch.nn.Linear(1, 1, bias=False)
+    tracker = GradSNRTracker(beta=0.5, eps=1e-8)
+
+    model.weight.grad = torch.tensor([[1.0]])
+    tracker.update(model)
+    model.weight.grad = torch.tensor([[3.0]])
+    tracker.update(model)
+
+    # E[g]^2 / Var(g) = 4 / 1 = 4, which is 6.0206 dB.
+    assert tracker.snr == pytest.approx(10.0 * torch.log10(torch.tensor(4.0)).item())