Add engine-debug-tools and fix critter animation rendering bugs

- engine-debug-tools/: a debug dump hotkey + dump2png to inspect
  decoded critter frames independent of the renderer (see root
  README.md's "Debugging" section).
- engine-patches/04,05: fix critter sprite scale and an OpenGL
  texture cache collision, found using that tooling.
- mdlp: fix encodeFrames RLE-diffing upscaled frames against a
  previous-frame reference the real RSD8 decoder never implements
  (verified against Night Dive's original Mac source down to the
  68K assembly) - was rendering as scattered static in-game.
- Upscale pipeline: better color quantization (dithering, pure-ramp
  exclusion) and per-resource model selection.

modding/src/animgallery/main.go

@@ -470,13 +470,13 @@ func writeIndex(path string, entries []galleryEntry) error {
 		`<label>Model: <select id="model">` +
 		`<option>realesrgan-x4plus-anime</option>` +
 		`<option>realesrgan-x4plus</option>` +
-		`<option>realesr-animevideov3</option>` +
+		`<option>realesr-general-x4v3</option>` +
 		`</select></label>` +
 		`<label>Scale: <input id="scale" type="number" value="2" min="1" max="4" style="width:4em"></label>` +
 		`<button id="clear-sel" type="button">Clear selection</button>` +
 		`<br><label>Filter: <input type="text" id="search" placeholder="id, language, file, transparent..." style="width:22em"></label>` +
 		`<span id="shown-count"></span>` +
-		`<textarea id="mdl-output" rows="12" readonly placeholder="Select animations below to generate an MDL upscale definition here - copy it into modding/mods/&lt;name&gt;/upscale/&lt;label&gt;.json"></textarea>` +
+		`<textarea id="mdl-output" rows="12" readonly placeholder="Select animations below to generate an MDL upscale definition here - copy it into modding/mods/&lt;name&gt;/bitmaps/&lt;label&gt;.json"></textarea>` +
 		`</div>`)
 
 	b.WriteString(`<h2>Selected (<span id="basket-count">0</span>)</h2><div id="basket"></div>`)