feat: add cherry-pick option and methods with tests

[racgoo]

Summary

Add cherry-pick support to the 'Repository' with tests.

Changes

• Add 'cherrypick' and 'cherrypick_commit' methods
• Add tests covering cherry-pick behavior

Notes

• 'cherrypick_commit' is provided for inspecting the resulting 'Index' of a cherry-pick operation without mutating the repository.
• The 'dryRun' option on 'cherrypick' simulates applying the cherry-pick to detect conflicts and feasibility, whereas 'cherrypick_commit' returns the computed index that would result from the operation.
• Both approaches run without side effects, but serve different purposes: validation ('dryRun') vs result inspection ('cherrypick_commit').

Closes #169

[vercel]

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[racgoo]

Hi @seokju-na ,
I’ve opened this PR, but the GitHub Actions didn’t run due to permission limitations.
Could you please re-run the CI for this PR?

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Project	Deployment	Review	Updated (UTC)
es-git	Ready	Preview, Comment	Dec 22, 2025 10:16am

[seokju-na]

Thanks!