New: Add WebGL renderer

[AlexIchenskiy]

This PR introduces an alternative WebGL renderer alongside the existing Canvas renderer, plus a refactor of the layout/simulator engine to support it. The Canvas renderer remains the default, WebGL is fully optional.

The goal is better rendering performance on larger graphs by offloading node/edge/label drawing to the GPU via custom GLSL shaders, and optionally running force-directed layout on the GPU as well.

What's included

• WebGL renderer (RendererType.WEBGL) — selectable per view, drawn with custom GLSL shaders for nodes, edges, and labels (src/renderer/webgl/).
• Node images & labels on the GPU — image atlas (image-atlas.ts) and label cache (label-cache.ts) so textures/text can be batched.
• Improved node/shape geometry options for the WebGL path.
• GPU force layout engine (gpu-force-layout-engine.ts) — runs the force simulation in WebGL2 with a quadtree/Barnes-Hut approximation. Automatically falls back to the CPU force engine if WebGL2 is unavailable.
• Layout engine refactor — the old d3-simulator-engine is replaced by a set of pluggable engines (force, circular, grid, hierarchical) behind a factory.

Documentation

Documentation for the WebGL renderer and the new layout engines is still lacking - the APIs may still change while this stabilizes, so docs will be filled in once everything is done and confirmed.

Usage

Opt into the WebGL renderer when creating a view:

const orb = new Orb.OrbView(container, {
  render: { type: 'webgl' },
});

Opt into GPU layout:

const orb = new Orb.OrbView(container, {
  render: { type: 'webgl' },
  layout: { type: 'force', options: { useGPU: true } },
});

Note on stability

This adds a WebGL rendering path, which should be considered experimental and potentially fragile. It depends on GPU/driver behavior and WebGL2 support, so rendering may differ across browsers, GPUs, parameters, and device pixel ratios, and can fail, look different or require cherry-picking for stable results where the Canvas renderer would not. The Canvas renderer remains the stable default and is unchanged in behavior.