Greatly expand Repl.py

This adds a few things I found from [this gist][1], but cleaned up quite a bit I
think, and designed a bit closer to the ghci user experience.

Along the way I figured out what ruff settings will autoformat my imports in one
alphabetized section, rather than splitting it into multiple sections for
builtins and external deps. So I made that change in the whole repo, but there
weren't too many changes.

[1]: https://gist.github.com/aliles/1153926

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