Switching to `pyproject.toml` for specifying package metadata

[matt-graham]

Switches from current setup.py approach of specifying package metadata to instead use a pyproject.toml configuration file and sets up setuptools_scm to automatically set package version number from Git release tags.

I think I've directly translated all the arguments passed to setup function in previous setup.py to equivalent pyproject.toml properties, so this should retain same metadata when publishing to PyPI, other than there was previously a slight typo in one argument (pacakge_data instead of package_data) which is now fixed. I've also added the additional requirements files as optional dependencies which can be installed with pip using the extras syntax, for example pip install s2fft[tests]. I also integrated the previous content in pytest.ini in to the pyproject.toml file.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.42%. Comparing base (2c3d9e5) to head (6bec4a5). Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
+ Coverage   93.10%   93.42%   +0.32%     
==========================================
  Files          29       28       -1     
  Lines        3146     3135      -11     
==========================================
  Hits         2929     2929              
+ Misses        217      206      -11     

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[matt-graham]

This PR is a dependency for #204 and we would ideally also merge before resolving #205 as then we can integrate the formatter configuration directly in to the pyproject.toml file, so tagging you for a review @CosmoMatt!

I've merged in latest changes from main (there was a conflict due to update of version specifier setup.py on main but we should be able to safely ignore this as version will be automatically derived from latest Git release tag when this goes in) and also removed the generated s2fft/_version.py file that was added in 95ea4f591650ef4a30970f059960977f5f8cc390 as this file shouldn't be version controlled (it will be generated on the fly at package installation by setuptools_scm based on current latest Git tag).

[CosmoMatt]

@matt-graham I had some issues here relating to healpy dropping support for older MacOS versions. I also ran into a version control issue relating to SciPy and healpy, a solution to which was just pinning the SciPy version. This should be fine for now, we'll just need to keep an eye on that in future.