sage.matroids: Update # needs, modularization fixes for imports

[mkoeppe]

📚 Description

• Many # optional are removed because small prime finite fields no longer need to be marked # optional/needs sage.rings.finite_rings since Integer.{perfect_power,is_prime_power,is_irreducible}: Handle easy cases without PARI #35847
• Other # optional are replaced by codeblock-scoped # needs tags
• Remaining # optional with standard features are replaced by # needs
• Some import fixes needed for separate testing of sagemath-modules or sagemath-graphs[modules] from Modularization of sagelib: Distributions sagemath-{brial,combinat,eclib,flint,gap,giac,glpk,graphs,groups,homfly,lcalc,libbraiding,libecm,linbox,modules,mpmath,ntl,pari,plot,polyhedra,schemes,singular,standard-no-symbolics,symbolics} #35095

This is:

• done with the help of sage -fixdoctests from Add style guide / reference for # optional - sage.... doctest tags, extend sage -t and sage -fixdoctests for modularization tasks #35749
• Part of: Meta-ticket: Modularize sagelib into separate distributions (pip-installable packages) sagemath-... for Sage 10.x #29705
• Cherry-picked from: Modularization of sagelib: Distributions sagemath-{brial,combinat,eclib,flint,gap,giac,glpk,graphs,groups,homfly,lcalc,libbraiding,libecm,linbox,modules,mpmath,ntl,pari,plot,polyhedra,schemes,singular,standard-no-symbolics,symbolics} #35095

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[dcoudert]

This is much lighter this way, in particular with the use of block statements like sage: # needs sage.graphs.

[dcoudert]

Why removing the indirect doctest statement ? Isn't it useful ?

[mkoeppe]

Thanks for catching this mistake. I've restored it in 4d11269

[dcoudert]

LGTM.

[mkoeppe]

Thank you!

[github-actions]

Documentation preview for this PR (built with commit 007f6ae; changes) is ready! 🎉