Move project configuration to pyproject.toml

[ecalifornica]

The du jour Python project metadata and configuration approach seems to have coalesced around using pyproject.toml, see PEP 621 and PEP 518.

This PR follows the documentation found at https://setuptools.pypa.io/en/latest/index.html to do the following:

• Moves most configuration metadata from setup.cfg to pyproject.toml, choosing to be explicit even when implicit pyproject.toml behavior matches the current configuration.
• Moves flake8 configuration to .flake8, as they do not support pyproject.toml.
• Removes the obsolete configuration zip_safe, see https://setuptools.pypa.io/en/latest/deprecated/zip_safe.html

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (8bde56c) 100.00% compared to head (d2bdc1d) 100.00%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #33 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 2 2 Lines 18 18 ========================================= Hits 18 18 ```

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