Add new debugging features to VAST tools

[lava]

This PR adds some new debugging features to lsvast and mdx-regenerate (which has been renamed to vast-regenerate) that are helpful when working with index- and mdx-files.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

[dominiklohmann]

Admittedly I didn't look at the code too much given that it's mostly debug tooling.

The lsvast changes I played with locally. They probably need to be adapted to include the changes from #2286 as well.

For vast-regenerate I'm worried about the complexity because we don't test whether it correctly uses the builders. Maybe we can (by default) cause it to write to a separate directory rather than replacing the files in-place?