Migrate to pyproject.toml

[MicahGale]

Description

Setuptools has deprecated installing via python setup.py install, though setup.py is not deprecated. The preferred method to install is python -m pip install ., which is the recommended method.

However, pyproject.toml is very much so the preferred way to configure a project over setup.py pytest.ini, etc.

In playing around with this pyproject.toml is not a full replacement of setup.py for OpenMC. This is because AFAIK there is not a way to get cython to work with pyproject.toml as of now.

Proposal:

• Move all configuration possible to pyproject.toml and delete pytest.ini.
• Keep setup.py as a minimum script to allow cython to work.

Alternatives

Do nothing. Likely, this will eventually lead to Deprecation warnings at some point but that is likely years away.

Compatibility

This should not change the user facing components at all. Some dependencies may need to be pinned to newer versions to add toml support.

I have started working on this as well as @shimwell.

[shimwell]

Awesome to hear. I remember we chatted a while back on slack about this.

Not sure if this helps but here is a pyproject.toml I threw together a while back. I think that I couldn't find out how to move everything across.

[MicahGale]

I also started something here, so we can just figure out how to merge these efforts.

[MicahGale]

This has been resolved by #3140, and other previous work.