proposal: switch to pyproject.toml structure

[dpaiton]

The Python org has advised that projects move away from requirements.txt and setup.py files and instead using pyproject.toml to define packages.

I propose we make this change now. I will do this if we have a consensus.

[belsten]

I think this is a good idea. There is also a docs/requirements.txt which is in the documentation branch I'm going to make a PR for soon. It would be helpful to add that to the toml.

What do you think @9q9q @HarrisonSantiago @ivanov ?

[HarrisonSantiago]

I'm a fan of the idea

[9q9q]

i'm on board, thanks dylan!