feat: Integrate custom prop library and sandbox functionality

- Added support for custom props in the sandbox, including loading, saving, and rendering.
- Implemented `PropLibrary` for managing custom prop entries and scanning for `.prop` files.
- Introduced `PropVisuals` for shared visual and collision representation of custom props.
- Enhanced `StageSpawner` to handle spawning of custom props with layered visuals and collision hulls.
- Created `MissingPropPlaceholder` to manage missing custom props during scene reloads.
- Updated thumbnail generation to support custom props with unique keys based on file paths.
- Added tests for custom prop lifecycle, authored visual values, and missing prop handling.
- Refactored existing code to accommodate new prop functionalities and ensure backward compatibility.

scripts/thumbnails/prop_thumbnail.gd

@@ -2,6 +2,7 @@ class_name PropThumbnail
 extends Node
 
 const PROP_BLOCK := preload("res://scripts/prop_block.gd")
+const PROP_VISUALS := preload("res://scripts/prop_visuals.gd")
 
 const SIZE := Vector2i(200, 200)
 
@@ -64,6 +65,20 @@ func render(payload: Dictionary, material_preset: int) -> Texture2D:
 	return ImageTexture.create_from_image(img)
 
 
+func render_shapes(shapes: Array[Dictionary]) -> Texture2D:
+	_clear_world()
+	var visual := Node2D.new()
+	_world.add_child(visual)
+	var bounds: Rect2 = PROP_VISUALS.build(visual, shapes)
+	_frame_camera(bounds if bounds.size.length_squared() > 0.0 else Rect2(Vector2(-24, -24), Vector2(48, 48)))
+	await RenderingServer.frame_post_draw
+	await RenderingServer.frame_post_draw
+	var tex := _viewport.get_texture()
+	visual.queue_free()
+	if tex == null or _is_blank(tex.get_image()): return null
+	return ImageTexture.create_from_image(tex.get_image())
+
+
 func _compute_points(payload: Dictionary) -> PackedVector2Array:
 	var shape_type: int = int(payload.get("type", PROP_BLOCK.ShapeType.POLYGON))
 	if shape_type == PROP_BLOCK.ShapeType.CIRCLE:

scripts/thumbnails/thumbnail_cache.gd

@@ -40,7 +40,9 @@ func prop_png(id: String) -> String:
 
 
 func prop_file_key(path: String) -> String:
-	return "%s_%d" % [path.get_file().get_basename(), FileAccess.get_modified_time(path)]
+	var canonical: String = path.simplify_path()
+	var digest: String = canonical.sha256_text().substr(0, 12)
+	return "file_%s_%d" % [digest, FileAccess.get_modified_time(path)]
 
 
 func prop_file_png(path: String) -> String: