Refactor depth reference handling and cleanup

- Unified reference depth calculation to use a single implementation in common/depth.py.
- Removed server-side reference depth computation and adjusted depth.json to only include image_size and intrinsics.
- Updated depth texture handling to ignore transparent, invalid, and non-positive pixels when calculating reference depth.
- Changed reference depth calculation to use the 95th percentile of valid depth values.
- Adjusted depth direction fitting to return a flat direction when no samples are available.
- Removed cleanup threshold parameters from Cutout and related nodes, simplifying the interface.
- Updated tests to verify new reference depth logic and ensure compatibility with existing functionality.

tests/anyimage/operators/test_cutout_operators.py

@@ -309,7 +309,7 @@ class CutoutOperatorsTest(BlenderTestCase):
             [operator.model],
         )
         self.assertTrue(parameters["generate_depth"])
-        self.assertEqual(parameters["alpha_threshold"], 0.25)
+        self.assertNotIn("alpha_threshold", parameters)
         self.assertEqual(parameters["normal_mode"], "OBJECT")