Migrate to pyproject.toml for modern packaging and editable installs

[mcyc]

Legacy editable installs (via setup.py develop) are deprecated and will be removed in pip 25.0. To future-proof the project and align with modern packaging standards, we need to migrate to using a pyproject.toml file as per PEP 660. This ensures compatibility with current and future versions of pip and setuptools.

Proposed Steps:

1. Add a pyproject.toml file with a minimal configuration:

   [build-system]
   requires = ["setuptools>=64", "wheel"]
   build-backend = "setuptools.build_meta"

2. Test the installation workflow:
   • Ensure editable installs (pip install -e .) work as expected.
   • Update documentation if necessary.
3. Remove reliance on legacy setup.py workflows in the future.

References:

• PEP 660
• pip issue #11457