Add `enabled` property to animations to toggle them on/off

[task-jp]

This adds an enabled boolean property to the animate block, which defaults to true. When set to false, property changes apply immediately without animation, bypassing duration, easing, and iterations.

• Added enabled field to PropertyAnimation struct
• Updated compiler to handle enabled property with proper defaults
• Added runtime check to skip animation when disabled
• Included comprehensive tests for static and dynamic enabled values
• Updated documentation and CHANGELOG

[tasuku-suzuki-signalslot]

Thank you for your review. I understood that this won't be useful until #348 is done. I'll try to fix #348 first.