refactor: scheduler without external libraries (backport #18331)

[mergify]

This is an automatic backport of pull request #18331 done by Mergify.
Cherry-pick of c3b547f has failed:

On branch mergify/bp/version-13-hotfix/pr-18331
Your branch is up to date with 'origin/version-13-hotfix'.

You are currently cherry-picking commit c3b547f897.
  (fix conflicts and run "git cherry-pick --continue")
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   frappe/utils/scheduler.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   pyproject.toml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[frappe-pr-bot]

🎉 This PR is included in version 13.57.3 🎉

The release is available on GitHub release

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