CSMShadowNode: Fix toggle of castShadow.

[Mugen87]

Related issue: #31183

Description

It was not possible so far to toggle the castShadow property of directional lights using CSMShadowNode.

AnalyticLightNode calls dispose() on shadow nodes that are not used anymore. CSMShadowNode uses its dispose() method to remove additions to the scene graph to make cascading work. If the instance of CSMShadowNode is now used again (because castShadow is set back to true), the state must be restored. The PR is doing this in updateBefore().

@sunag I have updated ShadowBaseNode by removing the dispose() method. Setting updateBeforeType to NodeUpdateType.NONE is an issue since when a shadow node is reused after a dispose, updateBefore() is never executed anymore. Because updateBefore() is not called when lights don't cast shadows, it seems better to not change updateBeforeType so shadow nodes don't have restore the update type on their own.

[Mugen87]

Globally toggling shadows was never an ideal solution. With this PR, CSM shadows can be toggled on light level which is way more intuitive (and practical).

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	337.26 78.64	337.26 78.64	+0 B +0 B
WebGPU	551.84 153.07	551.8 153.06	-40 B -9 B
WebGPU Nodes	551.19 152.91	551.15 152.9	-40 B -9 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	468.44 113.28	468.44 113.28	+0 B +0 B
WebGPU	626.86 169.75	626.82 169.74	-35 B -9 B
WebGPU Nodes	581.71 159.08	581.67 159.08	-35 B -8 B