test(compat/defer): Replace deprecated done() callback with fake timers in async tests

[miinhho]

Problem

Deprecation warning occurs when using the done() callback in Vitest tests

Solution

Replaced Vitest's deprecated done() callback with fake timers

Before

After

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Project	Deployment	Preview	Comments	Updated (UTC)
es-toolkit	Ready	Preview	Comment	Oct 29, 2025 4:45pm

[Copilot]

Pull Request Overview

This PR modernizes Vitest test implementation by replacing deprecated done() callback patterns with fake timers for asynchronous testing.

• Replaced deprecated done() callback usage with vi.useFakeTimers() and vi.advanceTimersByTime()
• Added proper test setup and teardown with beforeEach and afterEach hooks
• Simplified async test logic by eliminating callback-based patterns

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.88%. Comparing base (2687388) to head (efffda2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1360   +/-   ##
=======================================
  Coverage   99.88%   99.88%           
=======================================
  Files         468      468           
  Lines        4453     4453           
  Branches     1311     1311           
=======================================
  Hits         4448     4448           
  Misses          5        5           

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