c-bata

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@porink0424 Would you mind reviewing this PR instead of me?

@conda-forge/help-python this PR is ready for review. I think the CI will be fixed by re-run since all maintainers commented on this pull request now.

Sorry, I've noticed that docker build is failed due to the following error. I will address this issue and make this pr ready for review again. ``` Could not solve...

The CI failures seem to be caused by `ga4mp` being available only on PyPI and not registered on conda-forge, as indicated by the error message below: ``` Could not solve...

All CI checks have passed now. @conda-forge/help-python this PR is ready for review.

Let me change the label from `code-fix` to `enhancement` since this PR changes the behavior of Optuna without breaking changes.

@HideakiImamura @porink0424 Could you review this PR?