Use poetry for dependency management

[sea-kelp]

Description of Changes

Fixes #374. Use poetry for dependency management (Borrowing heavily from lucyparsons#893)

Notes for Deployment

• With this change, we won't automatically re-build scss files when they are updated anymore. (The nodejs build is completely done in a separate Docker build stage now) I don't think it's a big deal since we don't regularly update our styles.
• I did have to upgrade our pandas version since we were using a very old version. Please check that the data-mungers still work!

Screenshots (if appropriate)

N/A

Tests and linting

Ran unit tests and checked that development and prod instances run

• I have rebased my changes on main

• just lint passes

• just test passes

[sea-kelp]

Also tagging @michplunkett in case you want to copy this for upstream

[AetherUnbound]

This is awesome! It's nice to get rid of the entrypoint, and the multi-stage build makes a ton of sense. The pandas changes should be fine, as we're not doing anything too out there and the API hasn't changed significantly.

[AetherUnbound]

This is great!!

[michplunkett]

I'm torn between updating the main repository to Poetry or doing the new shiny thing and migrating it to uv. Poetry does make the most sense, but I am very drawn to the new shiny thing.