feat(selection): separate selection geometry from image content processing

- Introduced a new design for selection rasterization that decouples the selection geometry from the image content, ensuring that the SelectionMask is independent of the source image's alpha and color.
- Updated the `rasterize_selection_path` function to only accept selection paths and image dimensions, removing parameters related to source alpha and alpha thresholds.
- Implemented a new approach for handling selection paths using non-zero winding fill, ensuring overlapping areas are preserved.
- Enhanced performance by utilizing a scanline algorithm for rasterization, significantly reducing processing time for high-resolution images.
- Updated internal documentation and added comprehensive tests to validate the new behavior and performance improvements.
- Ensured backward compatibility by maintaining existing interfaces where necessary while introducing breaking changes in the selection processing logic.

src/anyimage/operators/cutout_tool/interaction.py

@@ -5,9 +5,6 @@ from ...preferences import (
     MIN_CUTOUT_MESH_RESOLUTION,
 )
 from ...properties import ai_ready
-from ...common.image import image_rgba
-from ...common.selection import rasterize_selection_path
-from .geometry import CUTOUT_ALPHA_THRESHOLD
 from .shape import CUTOUT_SHAPE_LABELS
 
 CUTOUT_SHAPE_BUTTONS = (
@@ -25,21 +22,6 @@ CUTOUT_MESH_DETAIL_SPACING = {
 }
 
 
-def validate_cutout_selection(
-    source_object,
-    selection_path,
-):
-    image = source_object.data
-    rgba = image_rgba(image)
-    rasterize_selection_path(
-        tuple(image.size),
-        selection_path,
-        source_alpha=rgba[:, :, 3],
-        alpha_threshold=CUTOUT_ALPHA_THRESHOLD,
-        antialias=True,
-    )
-
-
 def cutout_mesh_resolution(image_size, point_spacing):
     longest_edge = max(int(value) for value in image_size)
     detail = round(longest_edge / max(int(point_spacing), 1))