SkeletonHelper: Add setColors()

[lukehorvat]

Related issue: #23829 (comment)

Description

SkeletonHelper always defaults to green and blue line colors for each bone. These colors might be hard to see on some meshes, so it would be nice to have the option of setting custom colors.

I added a setColors( color1, color2 ) method for this purpose, modeled on the existing setColors methods of CameraHelper and AxesHelper.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.22 78.88	338.22 78.88	+0 B +0 B
WebGPU	560.22 155.1	560.22 155.1	+0 B +0 B
WebGPU Nodes	559.14 154.89	559.14 154.89	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.49 113.56	469.49 113.56	+0 B +0 B
WebGPU	635.38 172.03	635.38 172.03	+0 B +0 B
WebGPU Nodes	590.03 161.27	590.03 161.27	+0 B +0 B