Refactor image processing and cutout functionalities

- Updated the naming convention for upscaled images to include underscores and file extensions.
- Renamed properties related to cutout pixel size to point spacing for clarity.
- Adjusted alpha region calculations to use a half-alpha threshold for better accuracy.
- Enhanced the handling of foreground mesh masks to consider half-alpha values.
- Introduced new functions for unbounded selections and cutout images, ensuring proper handling of source and selection images.
- Improved test coverage for cutout functionalities, including bounds mapping and alpha preservation.
- Updated tests to reflect changes in naming conventions and functionality adjustments.

tests/test_worker.py

@@ -1428,12 +1428,17 @@ class WorkerTest(unittest.TestCase):
 
         np.testing.assert_array_equal(filtered, faces[[0]])
 
-    def test_surface_background_mask_keeps_any_nonzero_alpha(self):
+    def test_surface_background_mask_uses_half_alpha_threshold(self):
         from PIL import Image
 
         with tempfile.TemporaryDirectory() as temporary:
             root = Path(temporary)
-            for alpha, expected in ((0, False), (1, True), (127, True)):
+            for alpha, expected in (
+                (0, False),
+                (127, False),
+                (128, True),
+                (255, True),
+            ):
                 path = root / f"alpha-{alpha}.png"
                 Image.new("RGBA", (2, 2), (10, 20, 30, alpha)).save(path)
                 mask = self.geometry.foreground_mesh_mask(path, (2, 2))