DOC: Add note on inference behavior of apply with result_type='expand'

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Closes #61057

• This PR adds a docstring note about the inference behavior of apply with result_type='expand' when function returns NaN-like values, as discussed in issue #61057.
• Added docstring to distinguish behavior for 'apply' method.

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[datapythonista]

Personally I think we should deprecate that parameter. Since I guess you're using it, do you mind sharing an example of how you are using it?

You'll have to remove the blank lines for the PR. Also, did you check if what you are detailing is only affected by expand, or also by reduce?

[github-actions[bot]]

This pull request is stale because it has been open for thirty days with no activity. Please update and respond to this comment if you're still interested in working on this.

[mroeschke]

Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.