Ensure ConfigPaths and CliArgParser FFI use Vec<u8>/&[u8] for filepaths

[Minoru]

This is split from #2561 (review). On the feature/2326-filepath branch, we should look through rust/libnewsboat-ffi/ and fix all places where paths are passed as Strings.

This is part of #2326.

[dennisschagt]

I'm planning to implement this using the filepath::PathBuf, similar to the changes in #2652

[Minoru]

Somehow this wasn't auto-closed by #2653 which resolves this issue.

[dennisschagt]

The "magic" resolves ... text didn't work either so I added the link manually after opening the PR.
I guess that's just a Github behavior for PR's which don't go into the default (master) branch.

[Minoru]

Oh, you're totally right: https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword#linking-a-pull-request-to-an-issue-using-a-keyword

Note: The special keywords in a pull request description are interpreted when the pull request targets the repository's default branch. However, if the PR's base is any other branch, then these keywords are ignored, no links are created and merging the PR has no effect on the issues. If you want to link a pull request to an issue using a keyword, the PR must be on the default branch.

Live and learn :)