fix: canvas scaling quality, copyTransformTo, and pitch-preserving speed change

[PiedPiper911]

Summary

Three improvements to the WebAV canvas rendering and audio processing:

Fix #482 - Video blurs after manual scale-down

Set imageSmoothingQuality = 'high' in BaseSprite._render() before any drawing operations. The Canvas 2D API defaults to low-quality interpolation, which causes visible blurriness when high-resolution video is scaled down on the canvas.

This applies to all sprite types (VisibleSprite, OffscreenSprite) since they all call super._render(ctx) before drawImage().

Fix #481 - Text sprite bounding box doesn't follow after copyStateTo

Added a new copyTransformTo() method on BaseSprite that copies only position and rotation (x, y, angle) while preserving the target sprite's own dimensions (w, h).

The existing copyStateTo() behavior is unchanged for backward compatibility.

Fix #487 - Pitch-preserving speed change (SoundTouch integration)

Added SpeedAudioClip class and createSpeedAudioClip() factory function that wraps an AudioClip with SoundTouch time-stretching. This decouples playback speed from pitch:

• Native OffscreenSprite speed change: changes both speed AND pitch
• SpeedAudioClip: changes speed while keeping original pitch

soundtouch-ts is added as an optional peer dependency - dynamically imported only when SpeedAudioClip is used, so users who don't need this feature pay zero cost.

Usage:

import { AudioClip, OffscreenSprite, createSpeedAudioClip } from '@webav/av-cliper';

const audioClip = new AudioClip(audioSource);
const speedClip = createSpeedAudioClip(audioClip, 1.5); // 1.5x speed, pitch preserved

const sprite = new OffscreenSprite(speedClip);
sprite.time.playbackRate = 1; // Required: bypass OffscreenSprite's own resampling

Test plan

• Import a high-res video, scale it down on canvas - should be sharp, not blurry
• Create a text sprite, modify its text, use copyTransformTo() to transfer position - bounding box should follow correctly
• Verify copyStateTo() still works as before (copies all properties including dimensions)
• Install soundtouch-ts, create a SpeedAudioClip at 1.5x speed - audio should be faster but pitch unchanged
• Verify createSpeedAudioClip(clip, 1.0) returns the original clip (no overhead)