Function spritesheetLoader

spritesheetLoader<S extends SpritesheetData = SpritesheetData>(
url: string,
): () => Promise<Spritesheet<S>>
Build an asset-manager-compatible loader for a PixiJS spritesheet atlas (TexturePacker JSON, etc.). Returns the fully-parsed Spritesheet object with .animations and .textures populated.

The loader performs a runtime shape check on the resolved value — Assets.load<T> is purely nominal in PixiJS, so pointing this at a non-atlas URL would otherwise surface as a misleading 'animation not found' error deep in clipFromSheet/animationSetFromSheet. The shape check turns that into a load-time error with a clear message.

To get literal animation-name inference, declare S as an interface ... extends SpritesheetData (a type alias re-widens via SpritesheetData.animations's Dict<string[]> string index signature).
Type Parameters
- S extends SpritesheetData = SpritesheetData
Parameters
- url: string
Returns () => Promise<Spritesheet<S>>
Example
```
interface HeroData extends SpritesheetData {
    animations: { idle: string[]; walk: string[]; attack: string[] };
  }

  ecs.builder.withAssets(a => a
    .add('hero', spritesheetLoader<HeroData>('/hero.json'))
  );

  // Later:
  const sheet = ecs.assets.get('hero');           // Spritesheet<HeroData>
  const set = animationSetFromSheet('hero', sheet); // names inferred
```
- Defined in plugins/rendering/sprite-animation.ts:678