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.

res/run.sh

@@ -4,4 +4,7 @@
 set -euo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 export LD_LIBRARY_PATH="$(pwd)/lib${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
-exec ./systemshock "$@"
+# Not `exec`: piping through tee needs this script's own process to stay
+# around as the pipeline. `pipefail` (set above) still makes the script
+# exit with systemshock's own exit code, not tee's.
+./systemshock "$@" 2>&1 | tee "$(pwd)/systemshock.log"