Create dedicated CSS group

[tylerriccio33]

This is a 2-fold PR:

1. I created a group for css-inline package called css. This would be helpful because I often have to use the css inlining feature in ci, and i must document it as a dependency. However, carrying around selenium can be cumbersome in production, since it has some tough requirements of it's own.
2. Reworked the _try_import function call out the dependency group needed to install said dependency instead of the generic pip install command. This would encourage users to follow best practices and add the correct group instead of one-off installing it.

I did these things which are not crucial but development quality of life. Feel free to strike them from the commit!

• I added pre-commit commands in the Makefile so users can more easily install it.
• Added uv.lock to the git ignore so it won't get tracked by users developing/contributing with uv.
• Used uv to run the tests in the Makefile instead of generic pytest .... The old version would require users to activate the environment. Not sure if you want to keep this depending on your philosophy!