Adds support for animating child elements with optional staggered timing

Adds support for animating child elements with optional staggered timing via two new data attributes.

Features

• Child Element Animation: New data-scroll-children attribute
  • Use "true" to animate direct children
  • Use class name (e.g. "card") to animate any descendants with that class
• Staggered Animation: New data-scroll-children-stagger attribute (e.g. "0.1s")
  • Creates sequential animation effects with configurable delay

Improvements

• Enhanced debug visualization resistance to CSS conflicts
• Improved cleanup for animation timeouts

All changes maintain backward compatibility while providing more animation capabilities.

Adds visual debugging features

Added a new debugging feature that shows you your "threshold line" and your "trigger line" so you can more easily see when an animation will start.