fix: only animate properties defined by keyframes

[Xerrion]

Summary

Animations that don't define scale or translate keyframes (e.g. fadeIn/fadeOut) no longer override the frame's existing scale or position. This fixes visible "jumping" when frames have a user-configured scale other than 1.0.

Problem

ApplyToFrame unconditionally called SetScale(sc), ClearAllPoints()+SetPoint(), and SetAlpha(al) every animation tick. For animations without scale keyframes, sc defaulted to 1.0 via PROPERTY_DEFAULTS, forcing the frame to scale 1.0 regardless of its configured scale. On animation completion, onFinished callbacks would restore the correct scale - causing a visible snap.

Same issue with translate: alpha-only animations unnecessarily repositioned the frame every tick.

Changes

• Keyframe introspection: Animate() now scans keyframes to determine which properties the animation defines (hasScale, hasTranslate)
• Conditional application: ApplyToFrame only sets translate/scale when the animation defines those properties
• Relative scale: Scale is now applied as sc * originalScale instead of absolute sc. A keyframe scale=0.3 means "30% of original", scale=1.0 means "back to original"
• Conditional restore: Stop() only restores properties that were animated
• Alpha remains always animated for backward compatibility (slide animations rely on default alpha=1.0)

Backward Compatibility

Animation type	hasScale	hasTranslate	Behavior
fadeIn/fadeOut	false	false	Only alpha. Scale and position untouched.
slideInRight/moveUp	false	true	Position + alpha. Scale untouched.
zoomIn/bounceIn	true	false	Scale (relative) + alpha. Position untouched.
zoomInLeft/backInRight	true	true	All three properties animated.

No breaking changes for existing consumers.