sage.categories: Modularization fixes for imports

[mkoeppe]

📚 Description

We should be able to import Python modules from sage.categories even if implementation modules are not installed; that's the premise of the distribution sagemath-categories.
Here we make changes to avoid module-level dependencies on some higher-level functionality, such as symbolic functions, linear algebra, etc.

#35275 takes care of some other imports.

Part of

• Meta-ticket: Modularize sagelib into separate distributions (pip-installable packages) sagemath-... for Sage 10.x #29705

📝 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

[codecov-commenter]

Codecov Report

Patch coverage: 88.88% and project coverage change: -0.01 ⚠️

Comparison is base (f449b14) 88.62% compared to head (df0507d) 88.62%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35279      +/-   ##
===========================================
- Coverage    88.62%   88.62%   -0.01%     
===========================================
  Files         2148     2148              
  Lines       398653   398663      +10     
===========================================
- Hits        353308   353307       -1     
- Misses       45345    45356      +11     

Impacted Files	Coverage Δ
src/sage/categories/rings.py	77.37% <50.00%> (-0.41%)	⬇️
...age/categories/finite_complex_reflection_groups.py	79.12% <100.00%> (ø)
...ries/finite_dimensional_lie_algebras_with_basis.py	83.54% <100.00%> (+0.25%)	⬆️
src/sage/categories/loop_crystals.py	96.65% <100.00%> (+0.01%)	⬆️
src/sage/categories/pushout.py	89.49% <100.00%> (ø)

... and 29 files with indirect coverage changes

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[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 8722462

[kwankyu]

LGTM

[mkoeppe]

Thank you!