WebGPURenderer: add Texture state tracking to NodeMaterialObserver

[aardgoose]

Related issue: #29386

A race exists where a NodeMaterialObserver captures a texture's state and the texture image is loaded/changed.
This was exposed in the webgpu_postprocessing_pixel example using WebGL.

Add an equals() method to Texture() and use this, with compensation for version changes from Texture.needsUpdate().

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	686.07 169.79	686.07 169.79	+0 B +0 B
WebGPU	832.51 223.04	832.67 223.1	+164 B +57 B
WebGPU Nodes	832.02 222.92	832.18 222.98	+164 B +58 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.42 111.53	462.42 111.53	+0 B +0 B
WebGPU	529.98 142.77	530.14 142.82	+164 B +58 B
WebGPU Nodes	486.64 132.63	486.8 132.68	+164 B +54 B