refactor: prevent useExternalEvents effect from running on every render

[eunwoo-levi]

Description

The handlers object inside useExternalEvents is recreated via Object.entries().reduce() on every render. Since it is used as a dependency of useLayoutEffect, the effect runs on every render, causing unnecessary emitter.off/emitter.on cycles.

Changes

• Store events in a useRef to always reference the latest callbacks without triggering re-registration.
• Register stable handler functions on mount only (dependency: []), which delegate to eventsRef.current internally.
• Clean up listeners on unmount.

Motivation and Context

The previous implementation caused emitter.off → emitter.on on every render, which is wasteful and creates a brief window where events could be missed between unsubscribe and resubscribe.

How Has This Been Tested?

• Verified existing unit tests pass locally (36/36).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have performed a self-review of my own code.
• My code is commented, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

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Latest commit: 762a7dd

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