Apply default options for a CLI parent command when a sub command is parsed

[chalcolith]

Prior to this fix, parsing a sub-command proceeded before assigning defaults to the parent's options. This fix factors out the default processing so it can occur before parsing a sub command.

Fixes #4580

[ponylang-main]

Hi @chalcolith,

The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 4593.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[SeanTAllen]

@chalcolith this would close #4580, yes?

[SeanTAllen]

I am far from an expert on this code, but if CI passes, I am good with saying "I approve".

[chalcolith]

@chalcolith this would close #4580, yes?

Yes; I've updated the description.