WebGPURenderer: Fix getArrayBufferAsync race condition and ensure proper buffer sequencing

[RenaudRohlinger]

Fixed #29270

WebGL Errors:

• performance warning: READ-usage buffer was read back without waiting on a fence. This caused a graphics pipeline stall.
• GL_INVALID_OPERATION: A transform feedback buffer that would be written to is also bound to a non-transform-feedback target

WebGPU Error:

• Failed to execute 'mapAsync' on 'GPUBuffer': Buffer was unmapped before mapping was resolved.

Description

Resolved #29270 by re-binding immediately after the fencing operation and correctly unbinding buffers post-operation in the WebGL backend.

Additionally, removed the readBufferGPU caching system in the WebGPU backend, which could cause race conditions during stress tests on subsequent calls.

This contribution is funded by Segments.AI & Utsubo

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	685.4 kB 169.7 kB	685.4 kB 169.7 kB	+0 B +0 B
WebGPU	821.7 kB 220.7 kB	821.7 kB 220.7 kB	+42 B -11 B
WebGPU Nodes	821.2 kB 220.6 kB	821.3 kB 220.6 kB	+461 B +81 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462 kB 111.4 kB	462 kB 111.4 kB	+0 B +0 B
WebGPU	522.1 kB 140.7 kB	522.1 kB 140.6 kB	+42 B -20 B
WebGPU Nodes	478.7 kB 130.5 kB	478.8 kB 130.5 kB	-43.31 kB -22 B