sage.groups.perm_gps.partn_ref*: Modularization fixes

[mkoeppe]

📚 Description

partn_ref2 depends on sage.libs.gap.

We restore the independence of partn_ref from sage.libs.gap by creating a separate function for the case of PS_first_smallest with non-None partn_ref_alg in partn_ref2.

We also remove the compile-time dependency on flint.

• 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]

while True might be better.
Furthermore, this loop has no control on the max value of I . Isn't it safer to use a for loop combined with a else statement to raise an error in case break is never called ?

[mkoeppe]

I've made these (and other) style fixes.

I also tested with an assert i < PS.degree at the end of the while loops and ran the tests for the faulty random seed reported in https://groups.google.com/g/sage-release/c/4mtUN8Rz92o/m/FLXKh321BgAJ; the assertion held, so at least this is not related.

I don't think I want to put the assertion there permanently though

[github-actions]

Documentation preview for this PR (built with commit 526efac; changes) is ready! 🎉

[dcoudert]

LGTM.

[mkoeppe]

Thank you!