fix(losses): address review comments on buffer tests

- Add state_dict assertions to verify non-persistent=False contract
- Update test docstrings to use Verify... format

Signed-off-by: Oleksandr Sanin <alexaaander.sanin@gmail.com>

Author: AlexanderSanin

tests/losses/image_dissimilarity/test_global_mutual_information_loss.py

@@ -147,30 +147,36 @@ def test_ill_opts(self, num_bins, reduction, expected_exception, expected_messag
 
 class TestGlobalMutualInformationLossBuffers(unittest.TestCase):
     def test_gaussian_kernel_registers_buffers(self):
-        """preterm and bin_centers are registered as non-persistent buffers for gaussian kernel."""
+        """Verify gaussian kernel registers preterm and bin_centers as non-trainable, non-persistent buffers."""
         loss = GlobalMutualInformationLoss(kernel_type="gaussian")
         self.assertIn("preterm", loss._buffers)
         self.assertIn("bin_centers", loss._buffers)
         self.assertFalse(loss.preterm.requires_grad)
         self.assertFalse(loss.bin_centers.requires_grad)
         self.assertEqual(loss.bin_centers.ndim, 3)
+        state = loss.state_dict()
+        self.assertNotIn("preterm", state)
+        self.assertNotIn("bin_centers", state)
 
     def test_bspline_kernel_has_no_gaussian_buffers(self):
-        """b-spline kernel does not register gaussian-specific buffers."""
+        """Verify b-spline kernel does not populate gaussian-specific buffers."""
         loss = GlobalMutualInformationLoss(kernel_type="b-spline")
         self.assertIsNone(loss.preterm)
         self.assertIsNone(loss.bin_centers)
+        state = loss.state_dict()
+        self.assertNotIn("preterm", state)
+        self.assertNotIn("bin_centers", state)
 
     def test_gaussian_kernel_forward_correct(self):
-        """Gaussian kernel forward pass returns a scalar loss."""
+        """Verify gaussian kernel forward pass returns a scalar loss tensor."""
         pred = torch.rand(2, 1, 8, 8, dtype=torch.float32)
         target = torch.rand(2, 1, 8, 8, dtype=torch.float32)
         loss = GlobalMutualInformationLoss(kernel_type="gaussian")
         result = loss(pred, target)
         self.assertEqual(result.shape, torch.Size([]))
 
     def test_gaussian_buffers_move_with_module(self):
-        """Buffers move to the correct device when the module is moved with .to()."""
+        """Verify preterm and bin_centers buffers move to the target device with the module."""
         loss = GlobalMutualInformationLoss(kernel_type="gaussian")
         self.assertEqual(loss.preterm.device.type, "cpu")
         self.assertEqual(loss.bin_centers.device.type, "cpu")