Issue #34949: sage.{categories,matrix,structure}: Replace imports from sage.*.all for namespace packages

[mkoeppe]

Closes #34949

[codecov-commenter]

Codecov Report

Base: 88.59% // Head: 88.58% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (d905cc3) compared to base (05329f6).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35012      +/-   ##
===========================================
- Coverage    88.59%   88.58%   -0.02%     
===========================================
  Files         2140     2140              
  Lines       396998   397006       +8     
===========================================
- Hits        351740   351700      -40     
- Misses       45258    45306      +48     

Impacted Files	Coverage Δ
src/sage/categories/category.py	98.01% <ø> (ø)
src/sage/docs/instancedoc.py	0.00% <ø> (ø)
src/sage/env.py	88.00% <ø> (ø)
src/sage/misc/cython.py	70.35% <ø> (ø)
src/sage/misc/sageinspect.py	80.81% <ø> (ø)
src/sage/misc/superseded.py	99.01% <ø> (ø)
src/sage/categories/bialgebras.py	100.00% <100.00%> (ø)
src/sage/categories/chain_complexes.py	93.02% <100.00%> (+0.34%)	⬆️
src/sage/categories/coalgebras.py	100.00% <100.00%> (ø)
src/sage/categories/coalgebras_with_basis.py	97.77% <100.00%> (+0.10%)	⬆️
... and 51 more

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[tobiasdiez]

Tests fail with

sage -t --random-seed=119552442577065273759575227667889303090 sage/structure/element.pyx  # 6 doctests failed

[mkoeppe]

I've fixed this and updated all other uses as well. Let's see what Build&Test has to say now.

[mkoeppe]

Turns out the placement of # optional tags was not to blame, after all, it was just a bad import. But I'm glad I made these changes; I also fixed some missing # optional tags for follow-up lines in doctests.

[tobiasdiez]

LGTM. I'll leave this at "needs review" as someone else might want to have a look at it. Feel free to set it to "positive review" in a week or so.

[mkoeppe]

Thank you!

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: d905cc3