Add Black formatting to the Python Spotless checks

[HTHou]

Summary

• configure spotless-maven-plugin in the Python module to run black during validation
• add black to the Python build requirements used by the module venv
• reformat the existing Python sources, examples, and tests to match the enforced style

Testing

• mvn -DskipTests validate in python/
• mvn spotless:apply in python/

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.51%. Comparing base (7d308fe) to head (34337f5).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #770   +/-   ##
========================================
  Coverage    62.51%   62.51%           
========================================
  Files          705      705           
  Lines        42569    42569           
  Branches      6289     6289           
========================================
  Hits         26614    26614           
  Misses       14987    14987           
  Partials       968      968           

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