CLI

[riordan]

I found this project back in January through @mhkeller and also have a need for a fast Postgres/Parquet loading CLI.

• Make cli #30

Starting from @mhkeller's stub CLI, I tried to throw something together using a LLM (not a real rust dev; so I have no idea what I'm doing and feel free to reject on principle).

Would love some feedback on:

1. Whether this approach does what you'd expect (consumes a Parquet file as input, streams Postgres binary format out to be piped into psql copy)
2. How you'd want this to be tested
3. how you would want this integrated into the project (currently $ make build-cli, but if accepted should be part of the rest of the CI).