GLTFLoader abort signal integration with LoadingManager progress tracking

Goal: ensure that aborting a GLTFLoader request also updates LoadingManager progress and cleans up any associated callbacks.

Constraints: LoadingManager does not provide a built‑in abort mechanism; developers must manually attach an AbortSignal to each loader and manage progress events to avoid orphaned callbacks or memory leaks.

Questions: Should LoadingManager expose a way to forward an AbortSignal to all active loaders? How can developers guarantee that aborting a loader stops related LoadingManager events without leaving dangling callbacks? Is there a recommended timeout pattern that works uniformly across loaders that lack native AbortSignal support?