Performance optimizations

[bobnik]

Performance Optimizations

Summary: Speed up the app in general with fewer re-renders.

• Math optimizations: Replace Math.pow(x, 2) with x * x via new magnitude() utility. Function call overhead makes Math.pow ~10-20x slower than direct multiplication for squaring. This is called frequently in geometry calculations (distance, polar coordinates) so the savings add up.

• Faster deep cloning: Replace JSON.parse(JSON.stringify()) with structuredClone().structuredClone is a native browser API that's identical and faster.

• Memoize list rows: Add React.memo to LayerRow and EffectRow components. These re-render on every parent render even when their props haven't changed. With many layers/effects, this causes unnecessary work during drag operations and state updates.

• Stabilize callback references: Wrap event handlers in useCallback throughout LayerList, EffectList, ShapePreview, EffectPreview. Without this, new function references are created on every render, which makes React.memo useless on child components.