AudioLoader: Fix race condition with loading manager.

[Mugen87]

Fixed #10706.

Description

Another attempt to fix #10706. I've realized there is a much cleaner approach to fix the race condition in AudioLoader that potentially occurs when used with LoadingManager.

To recap: LoadingManager can fire too early when the audio isn't decoded yet so if you attempt to playback such an audio you run into runtime errors. However, by using a separate "decode item", it's possible to keep the LoadingManager waiting until the decode has finished.

This change requires no changes in FileLoader which was a blocker of previous PRs.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	361.21 85.78	361.21 85.78	+0 B +0 B
WebGPU	637.48 177.06	637.48 177.06	+0 B +0 B
WebGPU Nodes	635.59 176.76	635.59 176.76	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	493.58 120.42	493.58 120.42	+0 B +0 B
WebGPU	709.22 191.88	709.22 191.88	+0 B +0 B
WebGPU Nodes	658.44 179.17	658.44 179.17	+0 B +0 B