Run black formatter - outdated version for Python 3.9

[jerubball]

Recent merges had checks failing again.

I have run the black formatter, and also commented out unused import to have flake8 pass.

As pointed out in #1619, latest version of black==26.3.1 does not support Python 3.9.

We have two options that I can think of.

• One is to drop the Python 3.9 support, because it reached end of life on October 2025.

• Other is to set the black version in requirements-dev.txt file to black==25.11.0.

This PR only runs formatter, and does not implement the solutions above.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.58%. Comparing base (c924704) to head (ac98e7b).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1624      +/-   ##
==========================================
+ Coverage   42.09%   42.58%   +0.49%     
==========================================
  Files          66       66              
  Lines        8693     8668      -25     
  Branches     1064     1058       -6     
==========================================
+ Hits         3659     3691      +32     
+ Misses       4897     4841      -56     
+ Partials      137      136       -1     

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