Fix memory leak: replace JSDOM with lightweight DOM stub + graphics pool

[shakeelmohamed]

Problem

Running p5.js sketches that call createGraphics() every frame caused unbounded heap growth (76MB → 700MB+). Two root causes:

1. JSDOM — the full DOM implementation kept every canvas element alive in its internal node tree, preventing garbage collection.
2. Per-frame Cairo surface allocation — each createGraphics() call allocated a new native Cairo instance, they were were released and therefore never garbage collected.

Key Changes

p5b-dom.js (new file) — P5bDOM class with a minimal DOM stub we have full ownership over. It canvases so lifecycle is fully under our control. This DOM stub is not exported in the library’s public API.

p5b.js

• Replaced JSDOM with P5bDOM
• Added _gfxPool (Map keyed by WxH dimensions) — createGraphics() is overridden to return a pooled p5.Graphics object when one is available, making zero new Cairo allocations after the first frame
• toFrame() now uses Cairo’s native drawImage + toBuffer("raw") for scaling (BGRA→RGBA swap) instead of a JS pixel loop over the full source canvas
• Overrode p5.Graphics.remove() to safely detach from the DOM stub without crashing in headless environments
• Fixed _emitRuntimeError to always emit (was silently swallowing errors when no listener was attached)

package.json

• Added p5b-dom.js to files
• Removed jsdom dependency

Result

Heap memory stabilizes around 13–19MB (normal GC sawtooth), RSS tends to cap around 100–125mb before garbage collection kicks in. Previously heap memory grew monotonically at ~80KB/frame, and RSS memory grew several mb per second leading to OOM errors after a few hours.