v1.2.3 — Shared multi-instance rendering, signs, and the diff engine

v1.2.3 — Shared multi-instance rendering, signs, and the diff engine

Highlights

• Shared multi-instance rendering: the new SchematicRendererContext lets many
  renderers on one page share a single resource pack/atlas and Web Worker pool, and
  optionally drive every viewport through one WebGL context (render-and-blit) —
  removing per-instance asset duplication and the browser's live-context limit.
• On-demand rendering: the GPU now idles to 0 fps when the scene is static and renders
  at the display's refresh rate during interaction, cutting power and heat with no loss
  of smoothness.
• Sign rendering: standing, wall, and hanging signs render with vanilla-accurate
  geometry (board/stick/plank/chains) and baked text read from sign block-entity NBT.
• Schematic diff engine: compare two schematics into added / removed / changed /
  swapped buckets with distance and support metrics, plus preset-based fingerprints
  (powered by Nucleation).

Fixes

• Mobile crash fix: framebuffers are sized with a clamped device pixel ratio
  (maxPixelRatio, default 2), preventing WebGL context-loss crashes on high-DPI phones.
• Smoother interaction: retired the legacy adaptive-FPS cap that made the playground
  feel sluggish; interaction now runs at the full refresh rate.

Test suite

• Modernized the test-suite index and added a Shared Renderer demo and a Schematic Diff
  page (drag-and-drop a before/after pair).