Phase 1: Safety & performance foundation for Grid/Entity overhaul

- Fix Entity3D self-reference cycle: replace raw `self` pointer with
  `pyobject` strong-ref pattern matching UIEntity (closes #266)
- TileLayer inherits Grid texture when none set, in all three attachment
  paths: constructor, add_layer(), and .grid property (closes #254)
- Add SpatialHash::queryCell() for O(1) entity-at-cell lookup; fix
  missing spatial_hash.insert() in Entity.__init__ grid= kwarg path;
  use queryCell in GridPoint.entities (closes #253)
- Add FOV dirty flag and parameter cache to skip redundant computeFOV
  calls when map unchanged and params match (closes #292)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/regression/issue_254_tilelayer_texture_test.py

@@ -0,0 +1,67 @@
+"""Regression test for #254: TileLayer inherits Grid texture when none set."""
+import mcrfpy
+import sys
+
+def test_tilelayer_texture_inheritance():
+    """TileLayer without texture should inherit grid's texture on attachment."""
+    scene = mcrfpy.Scene("test254")
+    mcrfpy.current_scene = scene
+
+    # Create grid with texture
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    scene.children.append(grid)
+
+    # Create TileLayer WITHOUT texture
+    layer_no_tex = mcrfpy.TileLayer(name="terrain", z_index=0)
+    grid.add_layer(layer_no_tex)
+
+    # Verify it inherited the grid's texture
+    assert layer_no_tex.texture is not None, "TileLayer should inherit grid texture"
+    print("PASS: TileLayer without texture inherits grid texture")
+
+    # Create TileLayer WITH explicit texture
+    tex2 = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    layer_with_tex = mcrfpy.TileLayer(name="overlay", z_index=1, texture=tex2)
+    grid.add_layer(layer_with_tex)
+
+    # Verify it kept its own texture
+    assert layer_with_tex.texture is not None, "TileLayer with texture should keep it"
+    print("PASS: TileLayer with explicit texture keeps its own")
+
+def test_tilelayer_texture_via_constructor():
+    """TileLayer passed in Grid constructor should also inherit texture."""
+    scene = mcrfpy.Scene("test254b")
+    mcrfpy.current_scene = scene
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    layer = mcrfpy.TileLayer(name="base", z_index=0)
+
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160),
+                        layers=[layer])
+    scene.children.append(grid)
+
+    assert layer.texture is not None, "TileLayer in constructor should inherit grid texture"
+    print("PASS: TileLayer in constructor inherits grid texture")
+
+def test_tilelayer_texture_via_grid_property():
+    """TileLayer attached via layer.grid = grid should inherit texture."""
+    scene = mcrfpy.Scene("test254c")
+    mcrfpy.current_scene = scene
+
+    tex = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+    grid = mcrfpy.Grid(grid_size=(10, 10), texture=tex, pos=(0, 0), size=(160, 160))
+    scene.children.append(grid)
+
+    layer = mcrfpy.TileLayer(name="via_prop", z_index=0)
+    layer.grid = grid
+
+    assert layer.texture is not None, "TileLayer attached via .grid should inherit texture"
+    print("PASS: TileLayer via .grid property inherits grid texture")
+
+if __name__ == "__main__":
+    test_tilelayer_texture_inheritance()
+    test_tilelayer_texture_via_constructor()
+    test_tilelayer_texture_via_grid_property()
+    print("All #254 tests passed")
+    sys.exit(0)