feat: animated GIF covers with config toggle and focus-based pausing

- Add settings menu with 'Animate GIF covers' toggle (default: off)
- When enabled: extract all GIF frames via ffmpeg, build AnimatedTexture
- When disabled: extract first frame only (static ImageTexture)
- AnimatedTexture starts paused — unpauses only when card has focus
- Focus-based pausing via gui_focus_changed signal (walks up to GameCard)
- Parse GIF89a frame delays for accurate animation speed
- Cache invalidation when setting changes (no restart needed)
- Cache AnimatedTextures in memory to avoid re-extraction
- Bump to v0.1.13

plugin.json

@@ -1,7 +1,7 @@
 {
   "plugin.id": "itch-artprovider",
   "plugin.name": "itch.io Art Provider",
-  "plugin.version": "0.1.12",
+  "plugin.version": "0.1.13",
   "plugin.min-api-version": "1.1.0",
   "plugin.link": "https://forge.thergic.ar/jose/itchio-opengamepadui-artprovider-plugin",
   "plugin.source": "https://forge.thergic.ar/jose/itchio-opengamepadui-artprovider-plugin",