fix(android): remount event on overlap relayout to clear stale paint

[anton-patrushev]

Summary

• Android-only: include packed layout state (zIndex, xOffsetPercentage) in each EventItem key so the View remounts when overlap topology changes.
• Works around an Android paint-state bug where, after a sibling event is removed, the surviving event's style updates but the native View keeps the old paint (tappable but invisible).
• iOS uses CALayer and keeps the original stable key, so no remount cost there.

Ported from core-mobile patch @howljs+calendar-kit+2.5.6+026+fix-android-stale-paint-on-overlap-relayout.

Stacked on top of #26.

Test plan

• Android: place two overlapping events, delete the front one; verify the remaining event renders normally (was previously invisible-but-tappable).
• iOS: same scenario; verify no regression and no extra unmount/remount.