fix(core): defer focus events in _changeFocus to prevent re-entrancy

[ionfwsrijan]

Description

_changeFocus() emits blur and focus events synchronously. Any subscriber can call unregister(), which mutates _focusables and adjusts _currentIndex. After handlers return, _changeFocus unconditionally overwrites _currentIndex = newIndex with the original pre-unregister value, corrupting focus state.

Fix

Deferred event emission (Approach A): collect blur/focus events into a queue, update _currentIndex first, then flush events. This ensures any re-entrant unregister() or focusNext() calls see the finalized _currentIndex.

Tests

• unregister in blur handler does not corrupt _currentIndex
• unregister in focus handler does not cause out-of-bounds access
• re-entrant focusNext from focus handler does not corrupt state

Closes #1629

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Run ID: 0b8e0afc-8fca-4d76-b23f-6d1369b86e01

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Reviewing files that changed from the base of the PR and between 4b874c0 and 506fadb.

📒 Files selected for processing (2)

• packages/core/src/events/FocusManager.test.ts
• packages/core/src/events/FocusManager.ts

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[ionfwsrijan]

@Karanjot786 Please review this