refactor: optimize snake sprite rendering using preloaded directional assets and implement HUD caching

AGENTS.md

@@ -179,7 +179,9 @@ The repository includes preconfigured tasks in [`.vscode/tasks.json`](.vscode/ta
 ### 6.2 Asset Pipeline
 - **Graphics Pipeline:**
   - [`gfx/tilemap.png`](gfx/tilemap.png) + [`gfx/tilemap.grit`](gfx/tilemap.grit) are processed by `grit` into `${CMAKE_CURRENT_BINARY_DIR}/tilemap.s` and `tilemap.h`.
-  - Sprites are referenced by index: tile 1 (segment), 2 (small segment), 3 (head), 5/6 (apple flash frames), 7/8/9/10 (tail variations), 11 (rotten apple).
+  - Sprites are referenced by index: tile 1 (segment), 2 (small segment), 3 (head horizontal), 4 (head vertical), 5/6 (apple flash frames), 7/8/9/10 (tail variations), 11 (rotten apple). All 12 sprite tiles are preloaded once into VRAM at startup; directional and blinking variants are rendered via pointer selection and hardware flipping flags without mid-frame DMA transfers.
+  - Active OAM sprites are clamped at hardware limit (128) and trailing unused sprites are hidden every frame via `oamClear(&oamSub, oamId, 128 - oamId)`.
+  - Console text HUD rendering in `draw_stats()` is throttled via dirty-flag caching (`HudCache`), eliminating redundant `iprintf` calls on VBlank.
 - **Audio Pipeline:**
   - Audio files in [`sounds/`](sounds/) are compiled by `mmutil` into `soundbank.bin` and header `soundbank.h`.
   - `bin2s` embeds `soundbank.bin` into assembly source `soundbank_bin.S` and header `soundbank_bin.h`.