refactor(grid): GridData is a map, not a widget -- delete UIGrid's drawable half

closes #361
closes #370
closes #371

UIGrid inherited both UIDrawable and GridData, so every map carried a second
camera and RenderTexture that nothing on screen corresponded to. Appending a
_GridData to a scene drew the whole map again through that ghost, frozen at
construction values. GridData is now pure data -- no position, no size, no
render() -- and UIGridView is the only widget.

UIGrid is deleted rather than demoted: shedding UIDrawable left an empty
subclass whose only job was to be what an aliasing shared_ptr pointed into.
GridData absorbs the texture (it defines the cell size, which every tile<->pixel
conversion depends on) and its own PythonObjectCache serial; the binding layer
becomes struct PyGridData. PyObjectsEnum::UIGRID and its 14 case arms go with it.

  * mcrfpy.GridData is public and standalone-constructible. A map with no view
    at all -- an offscreen level, still steppable and pathable -- was previously
    undefined behavior: GridData::markDirty did static_cast<UIGrid*>(this).
  * UIGridView::init constructs the GridData directly instead of building a
    throwaway Python _GridData, stealing its base subobject, and copying ~15
    fields of rendering state out of the discarded wrapper. One init() serves
    both modes, so a second view is no longer a crippled kwarg subset
    (Grid(grid=other, z_index=5) used to raise TypeError).
  * entity.grid returns the GridData. Accepted break: an entity may be on a map
    with no view or with several, so "the grid an entity is in" is not a camera.
    Migrate player.grid.center_camera(p) -> view.center_camera(p).
  * tp_name is mcrfpy.GridView; mcrfpy.Grid is an alias to the same type object.

Two latent bugs surfaced and are fixed here:

  #370  Grid.center_camera() and Grid.size = ... were SILENT NO-OPS -- neither
        was defined on the view, so both delegated to the ghost camera. On
        master, center_camera((5,5)) leaves center_x at 50.0.
  #371  The shader uniform binder strcmp'd tp_name == "mcrfpy.Grid" (the VIEW's
        name) then cast to PyUIGridObject. UB that only worked because both
        wrappers had identical layout and both classes put UIDrawable at offset 0.

Suite 327/327.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/regression/issue_359_shared_griddata_test.py

@@ -30,12 +30,13 @@ cameras over one dataset):
       dead property is gone, not silently still None.
 
 Design note carried over from the fix: GridData::views is a *list*, not a
-single pointer, specifically because N views can share one GridData. Index 0
-is guaranteed (by construction: a fresh GridData is only ever produced by
-Grid()'s factory path, `init_with_data`; `init_explicit_view` can only ATTACH
-to an already-existing GridData) to be the view that created the data, so
-UIEntity.grid identity (test 2) stays deterministic even with secondary
-views registered -- not an arbitrary pick from an unordered set.
+single pointer, specifically because N views can share one GridData.
+
+#361 update: entity.grid no longer returns a view at all -- it returns the
+GridData. The "which view is primary?" question that views.front() answered for
+identity purposes is gone, because the answer was always arbitrary dressed up as
+deterministic. The registry itself remains, and is still load-bearing for
+dirty-notification fan-out (test 3).
 """
 import sys
 import os
@@ -95,18 +96,20 @@ def test_1_two_views_render_shared_mutations():
 
 
 def test_2_entity_grid_identity():
-    """entity.grid returns the SAME object as the Grid() that actually
-    created the data (GridData::views.front()), not the secondary view, not
-    None, and not a fresh throwaway wrapper -- even once a secondary view is
-    registered on the same GridData."""
+    """entity.grid is the shared GridData -- one stable object, the same one both
+    views are looking at, and NOT either view (#361)."""
     print("(2) entity.grid identity with a secondary view registered...")
     grid_a = mcrfpy.Grid(grid_size=(5, 5))
-    grid_b = mcrfpy.Grid(grid=grid_a, pos=(0, 0), size=(80, 80))  # noqa: F841 (keep alive)
+    grid_b = mcrfpy.Grid(grid=grid_a, pos=(0, 0), size=(80, 80))
 
     e = mcrfpy.Entity((1, 1), grid=grid_a)
 
-    assert e.grid is grid_a, f"entity.grid identity broken: {e.grid!r} is not grid_a ({grid_a!r})"
-    assert e.grid is not grid_b, "entity.grid returned the secondary view instead of the creator"
+    data = grid_a.grid_data
+    assert grid_b.grid_data is data, "the two views do not share one GridData"
+    assert e.grid is data, f"entity.grid identity broken: {e.grid!r} is not {data!r}"
+    assert e.grid is e.grid, "entity.grid is not stable across reads"
+    assert e.grid is not grid_a and e.grid is not grid_b, \
+        "entity.grid returned a view; it must return the map (#361)"
     print("    OK")