large partial pep cleanup in cluster_seed

[fchapoton]

📚 Description

This tickets fixes many pep8 style warnings in the modified file.

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.
• I have linked an issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[fchapoton]

thanks, done

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 15f32f7

[codecov-commenter]

Codecov Report

Patch coverage: 93.36% and project coverage change: +0.02 🎉

Comparison is base (52a81cb) 88.57% compared to head (15f32f7) 88.60%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35228      +/-   ##
===========================================
+ Coverage    88.57%   88.60%   +0.02%     
===========================================
  Files         2140     2140              
  Lines       397273   397415     +142     
===========================================
+ Hits        351891   352116     +225     
+ Misses       45382    45299      -83     

Impacted Files	Coverage Δ
src/sage/schemes/elliptic_curves/ell_generic.py	93.11% <66.66%> (-0.12%)	⬇️
...ge/combinat/cluster_algebra_quiver/cluster_seed.py	85.05% <84.90%> (ø)
src/sage/interfaces/tachyon.py	87.93% <90.00%> (+0.43%)	⬆️
src/sage/schemes/elliptic_curves/gal_reps.py	82.23% <90.00%> (+0.04%)	⬆️
src/sage/quadratic_forms/quadratic_form.py	90.26% <95.65%> (+0.16%)	⬆️
src/sage/modular/quasimodform/element.py	99.20% <100.00%> (+0.06%)	⬆️
src/sage/rings/qqbar.py	95.30% <100.00%> (+<0.01%)	⬆️
src/sage/schemes/affine/affine_morphism.py	90.33% <100.00%> (ø)
src/sage/schemes/elliptic_curves/BSD.py	43.75% <100.00%> (+0.21%)	⬆️
src/sage/schemes/elliptic_curves/cardinality.py	87.54% <100.00%> (+0.93%)	⬆️
... and 70 more

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