fix: correct click percentage and listener removal

[chrisweb]

Summary

Fixes two bugs in the waveform canvas click handling (src/library/core.ts).

1. Click percentage is wrong on a CSS-scaled canvas

_canvasElementClick measured the click offset in CSS pixels (getBoundingClientRect()) but divided by canvas.width, which is the internal pixel resolution set in draw() (e.g. 200 * 2 + 199 * 1 = 599px for 200 peaks).

When the canvas is scaled with CSS (e.g. width: 100%), the rendered width and canvas.width differ, so the reported percentage is off and the error grows toward the right edge — a click at the far right of a 300px-wide canvas reports 300 / (599/100) ≈ 50% instead of 100%.

The fix divides by the rendered width from getBoundingClientRect().width, which matches the README's stated behaviour (position relative to the rendered canvas width) and is correct regardless of internal resolution / devicePixelRatio. Guards against a zero rendered width.

2. Click listener is never removed on destroy()

_removeClickWaveListener() called this._canvasElementClick.bind(this) again — a new function reference — so removeEventListener never matched the listener added by _addClickWaveListener(). The listener leaked, and consumers that re-create a Waveform on the same canvas accumulated handlers.

The bound handler is now stored once (_boundCanvasElementClick) and reused for both add and remove.

Testing

• npm run lint passes
• tsc --noEmit on src/index.ts (strict) passes

(npm run build fails locally on a missing tslib, unrelated to this change.)