Add UIInteractiveSpriteWidget for clickable sprites in UI

[pvcraven]

Summary

• Adds UIInteractiveSpriteWidget — combines UIInteractiveWidget + UISpriteWidget via multiple inheritance to make sprites clickable/hoverable in the UI tree
• Widget size defaults to sprite texture dimensions, overridable with explicit width/height
• Inherits full interactive behavior: hovered, pressed, disabled states, on_click event dispatch, keyboard/controller support
• Inherits sprite rendering: do_render() draws the sprite, on_update() calls sprite animation updates
• Exported from arcade.gui as public API

Test plan

• Click on sprite fires on_click event with correct source
• Click outside does not fire
• hovered updates on mouse enter/leave
• pressed is True between press and release
• disabled=True blocks click events
• Widget rect defaults to sprite texture size
• Explicit width/height overrides sprite size
• Works inside UIBoxLayout and UIAnchorLayout
• Callback via push_handlers(on_click=...) works
• Callback via widget.on_click = callback works
• All 349 existing GUI tests pass

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