Support for skip gestures

Improvements

• Introduced SkipTracker to simplify the implementation of skip gestures.
• Added skip methods that accept a Skip direction as a parameter. These methods are more ergonomic when the skip direction is determined programmatically, while the existing methods remain well-suited for UI-bound actions.
• Made PlayerItem conform to Hashable, simplifying the adoption of Hashable in wrapper types.
• Added methods to stop or close Picture in Picture without triggering restoration behavior.
• Added methods to show or hide the user interface managed by a VisibilityTracker.

Breaking Changes

• Core extensions previously defined on Array have been moved to Collection for broader applicability.
• Removed the PictureInPicturePersistable.pictureInPictureDidClose() method.

Demo Improvements

• Enabled support for skip gestures in the custom player layout.
• Improved playlist management UI in the demo: it now supports inserting the same item multiple times, with control over both the insertion point and a multiplier.
• URIs in the monitoring panel are now displayed in full without truncation.

Demo Fixes

• Fixed high-speed capsule display issues on devices with a notch.