Fix the type, macro and state-table defects, and the leftover debris

Closes internal-consistency items 19 through 36, 38 and 41. Item 37, the ~180
redundant casts, is deliberately left open with its reasoning in TODO.md: the
benefit only arrives once the build turns on the warnings those casts suppress,
and doing it before that is churn across the two files with the most
outstanding functional defects.

The two that were real bugs are in the actor state table.
AKGL_ACTOR_STATE_STRING_NAMES was declared [AKGL_ACTOR_MAX_STATES+1] and
defined [32], so a consumer trusting the declared bound read past the object;
and indices 11 and 12 were named UNDEFINED_11 and UNDEFINED_12 where actor.h
has MOVING_IN and MOVING_OUT, so no character JSON could bind a sprite to
either state. tests/registry.c now walks the whole table -- every entry
non-NULL, every entry resolving to its own bit, no two entries sharing a name.

The bitmask macros are parenthesized and AKGL_BITMASK_CLEAR has lost the
semicolon inside its body. Writing tests/bitmasks.c for that turned up
something worth knowing: the obvious test does not catch it. For a bit that is
set, the misparse `!(mask & bit) == bit` gives the same answer as the correct
one. It only diverges for an unset bit whose value is not 1, and that is the
shape the suite uses now.

akgl_draw_background was the last public function outside the error protocol.
It takes a backend like everything else in draw.h, restores the draw colour it
found, and is tested -- TODO.md had it filed under "needs the offscreen
renderer harness", which was never true; what it needed was to stop reading the
global.

All eight registry initializers go through one helper, so the seven that leaked
an SDL_PropertiesID on every call after the first no longer do. Fixed in the
same place because it is the same function: akgl_registry_init never called
akgl_registry_init_properties, which made akgl_set_property a silent no-op for
anyone not going through akgl_game_init -- Defects, Known and still open item 3.

Also: AKGL_COLLIDE_RECTANGLES (three open parens, two closes) and akgl_Frame
deleted, float32_t/float64_t used consistently, the developer-specific debug
logging removed from the controller inner loop, the abandoned SDL_GetBasePath
comments removed, nine unused locals removed, and dst renamed to dest.

akgl_game_update's default flags no longer OR the same bit twice. That changes
nothing today, and the reason is Performance item 32: the loop never reads
either bit, which is why every actor is updated sixteen times a frame. Still
open.

25/25 pass, memcheck clean, reindent --check clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

include/akgl/draw.h

@@ -39,18 +39,27 @@
 /**
  * @brief Paint an 8x8 grey checkerboard over a region, the way an image editor shows transparency.
  *
- * A diagnostic backdrop, not a general primitive -- `charviewer` uses it so a
- * sprite's transparent pixels are visible rather than blending into black. It
- * is the one function in this file that does not follow the file's conventions:
- * it draws through the *global* `akgl_renderer` rather than a backend the caller
- * passes in, it leaves the renderer's draw colour changed, and it reports
- * nothing.
+ * A diagnostic backdrop rather than a general primitive -- `charviewer` uses it
+ * so a sprite's transparent pixels are visible instead of blending into black.
  *
- * @param w Width of the region to cover, in pixels, starting at x = 0.
- * @param h Height of the region, starting at y = 0. Both round up to whole 8px
- *          cells, so a 12-pixel height paints 16.
+ * Until 0.5.0 this was the one function in the library outside the error
+ * protocol: it returned `void`, drew through the *global* `akgl_renderer`
+ * without checking it, and left the renderer's draw colour changed. It now
+ * takes a backend like every other entry point here and restores the colour it
+ * found, which is also what makes it testable without a world.
+ *
+ * @param self The backend to draw through. Required, along with its
+ *             `sdl_renderer`.
+ * @param w    Width of the region to cover, in pixels, starting at x = 0. Zero
+ *             or negative paints nothing and is not reported.
+ * @param h    Height of the region, starting at y = 0. Both round up to whole
+ *             8px cells, so a 12-pixel height paints 16.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER If @p self or `self->sdl_renderer` is `NULL`.
+ * @throws AKGL_ERR_SDL If the draw colour cannot be read or set, or a cell
+ *         cannot be filled.
  */
-void akgl_draw_background(int w, int h);
+akerr_ErrorContext AKERR_NOIGNORE *akgl_draw_background(akgl_RenderBackend *self, int w, int h);
 
 /**
  * @brief Plot a single pixel.