refactor(usePrevious): remove undefined from compare argument and return type

[wo-o29]

Overview

This PR updates both the code and documentation for the usePrevious hook to remove undefined from the compare function's argument types and from the return type.

Since the state parameter passed to the hook is a required value and always provided, and the initial state is stored in prevRef, the prev argument never becomes undefined during the hook's lifecycle. Thus, the hook also never returns undefined.

This update ensures consistency between implementation, type definitions, and documentation, clarifying the intended usage.

Before	After

Checklist

• Did you write the test code?
• Have you run yarn run fix to format and lint the code and docs?
• Have you run yarn run test:coverage to make sure there is no uncovered line?
• Did you write the JSDoc?

[Copilot]

Pull Request Overview

This PR refactors the usePrevious hook to remove undefined from both the compare function's argument types and the return type, making the type definitions more accurate to reflect the actual behavior where the hook always returns a value of type T.

• Updated type signatures to remove undefined from compare function parameter and return type
• Updated documentation in both English and Korean to reflect the corrected types
• Modified the default comparison function to match the new type signature

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/hooks/usePrevious/usePrevious.ts	Updated type signatures and JSDoc comments to remove undefined types
src/hooks/usePrevious/usePrevious.md	Updated documentation interface to reflect corrected types
src/hooks/usePrevious/ko/usePrevious.md	Updated Korean documentation interface to reflect corrected types

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5bdb4ff) to head (57bbf08).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           37        37           
  Lines         1093      1093           
  Branches       324       324           
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  Hits          1093      1093           

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[kimyouknow]

@wo-o29 Good catch — prev can never be undefined since useRef<T>(state) initializes it.
The type fix correctly reflects the implementation.

One note for future reference: on first render, usePrevious returns the current state (not undefined). This is by design but unusual for "previous value" hooks. Consider adding a JSDoc note about this.

Before merging, could you please add a changeset (yarn changeset) for this change? Since it modifies the public type signature, it should be tracked in the changelog.

Once the changeset is added, we'll merge! ✅