feat(eslint-plugin): add prefer-useloader rule

[travisbreaks]

Summary

Implements the prefer-useloader rule from the ESLint plugin RFC (#2701).

• Flags .load() and .loadAsync() calls inside useEffect/useLayoutEffect
• Recommends useLoader for automatic Suspense integration and caching
• Added to both recommended and all configs
• 10 test cases (5 valid, 5 invalid), all passing
• Docs with incorrect/correct examples

This picks up from where #2724 left off (closed unmerged). No overlap with the no-clone-in-loop / no-new-in-loop rules already landed in #2710.

Why prefer useLoader?

Calling Loader.load() or Loader.loadAsync() inside effects bypasses React Suspense boundaries and the built-in caching that useLoader provides. This is one of the most common R3F pitfalls, documented in the pitfalls guide.

Test plan

• All 21 existing + new tests pass (yarn test in eslint-plugin)
• Codegen ran clean (configs, index, README updated)
• Rule correctly ignores .load()/.loadAsync() outside effects
• Rule catches violations in both useEffect and useLayoutEffect
• Multiple violations in a single effect reported individually

Partial close of #2701.

Co-Authored-By: Claude Opus 4.6 (1M context) tadao@travisfixes.com

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[DennisSmolek]

The problem is that many dynamic systems use effects or other things to load textures later in runtime. Triggering suspense might switch to a fallback causing a blink or even a entire section to unload depending on where the boundry is placed.
Also this wouldnt catch useCallback functions called within the effect. I would need to see a test of loading something that takes some time dynamically and if it unloads the existing asset while waiting.

[travisbreaks]

Friendly ping. Let me know if this needs any changes or if there's anything blocking review.

[travisbreaks]

Good point. useLoader triggers Suspense, so for dynamic runtime loading (swapping textures mid-scene, progressively loading based on interaction), suspending could unmount existing content while the new asset loads.

The rule targets the common case where someone loads at mount time via useEffect out of habit. For dynamic loading, an eslint-disable makes sense.

Worth adding a "When not to use" section to the docs? Or would a rule option like allowDynamicLoading be more useful?