Fix #839 and move most `setup.py` metadata and config into `pyproject.toml`

[mhucka]

This addresses deprecation warnings originating from the use of outdated setuptools functions. I took this opportunity to modernize the package definition in accordance with current Python packaging standards (PEP 621).

Key changes include:

• All declarative package metadata (e.g., name, version, dependencies, author, classifiers) has been moved from setup.py to pyproject.toml.
• The setup.py file has been simplified to only contain the logic necessary for building the C++ extensions.
• The deprecated self.distribution.get_version() method has been replaced with a direct use of the __version__ variable.
• The py.typed marker file is now correctly included in the package via the [tool.setuptools.package-data] configuration in pyproject.toml.

This should fix #839 and also set the stage for using pyproject.toml to add more metadata and project configuration settings.

(I used Jules to help with this.)