Update license in pyproject.toml

[adtzlr]

This fixes #953. Change the declaration of the license and license file. See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.23%. Comparing base (8574f6a) to head (e12f639).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #954   +/-   ##
=======================================
  Coverage   97.23%   97.23%           
=======================================
  Files         183      183           
  Lines        6618     6618           
=======================================
  Hits         6435     6435           
  Misses        183      183           

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