feat: ✨ colorize output of explain() via rich (#244)

# Description

Rich's print function automatically colors different types of of
variables and some markup. A first step towards
#211, where
more specific improvements can be discussed further.

Needs a quick review.

## Checklist

- [ ] Formatted Markdown
- [x] Ran `just run-all`

---------

Co-authored-by: Luke W. Johnston <lwjohnst86@users.noreply.github.com>

Author: joelostblom