Every key call (removeKey, keyTime, keyValue, setInterpolationTypeAtKey…)
looked its key up through `__keys()`, which serialised the whole key list,
eases and tangents included, on each call. Removing keys one by one was
therefore quadratic: about 100 ms per removeKey on a 2,000-key property.
The `keys` query now takes an optional `index` and returns just that key
with the count; `__key` uses it. removeKey on 2,000 keys drops from
103.7 ms to 0.4 ms (release, Windows 11 aarch64).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
