libgap: Remove some GC hazards

[collares]

📚 Description

Trac branch u/gh-collares/gap-gc from #34701, now migrated to GitHub. Currently based atop #35093; will rebase once that is merged.

The rest of the description below is copied from #34701:

A refactor in #27946 introduced "unprotected" (not surrounded by GAP_Enter/GAP_Leave) GAP_ValueGlobalVariable calls. I believe this might be a GC hazard, because after updating to GAP 4.12.1 I started seeing aarch64 crashes on NixOS infrastructure such as:

#0  0x0000fffff79740e8 in wait4 ()
#1  0x0000fffff5dc6b78 in print_enhanced_backtrace ()
#2  0x0000fffff5dc8190 in sigdie ()
#3  0x0000fffff5dcb1c0 in cysigs_signal_handler ()
#4  0x0000fffff7ffb7cc in __kernel_rt_sigreturn ()
#5  0x0000ffff99a0bf28 in ConvString ()
#6  0x0000000000000000 in ?? ()
#7  0x0000000000000000 in ?? ()
#8  0x0000000000000000 in ?? ()
#9  0x0000ffff99989930 in Pr ()
#10 0x0000ffff9998aa18 in CloseOutput ()
#11 0x0000ffff99884828 in capture_stdout () at /build/sage-src-9.7/pkgs/sagemath-standard/sage/libs/gap/element.pyx:154
...

I also see cases where capture_stdout throws errors such as sage.libs.gap.util.GAPError: Error, Length: <list> must be a list (not the integer 255) and then crashes. Both types of errors are fixed by this ticket.

Note that I am nesting GAP_Enter/GAP_Leave calls because I didn't remove the preexisting calls inside capture_stdout. That's because I feared removing the innermost calls might create a new footgun (and I believe nested GAP_Enter/GAP_Leave calls are explicitly supported), but removing them should cause no problem. Removing them might even be preferable for performance reasons, I don't know.

Fixes #34701

📝 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

• update GAP to 4.12.2 #35093: GAP 4.12.2 upgrade, which touches the same function and should land first.

[dimpase]

lgtm

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (52a81cb) 88.57% compared to head (d458e35) 88.58%.

❗ Current head d458e35 differs from pull request most recent head 5f9d256. Consider uploading reports for the commit 5f9d256 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35114      +/-   ##
===========================================
+ Coverage    88.57%   88.58%   +0.01%     
===========================================
  Files         2140     2140              
  Lines       397273   396964     -309     
===========================================
- Hits        351891   351660     -231     
+ Misses       45382    45304      -78     

Impacted Files	Coverage Δ
src/sage/coding/linear_code.py	81.12% <ø> (ø)
src/sage/combinat/posets/posets.py	93.98% <ø> (+0.11%)	⬆️
...mbinat/root_system/hecke_algebra_representation.py	93.11% <ø> (ø)
src/sage/combinat/symmetric_group_algebra.py	94.35% <ø> (ø)
src/sage/groups/finitely_presented.py	95.88% <ø> (ø)
src/sage/groups/fqf_orthogonal.py	88.48% <ø> (ø)
src/sage/groups/matrix_gps/finitely_generated.py	90.50% <ø> (ø)
src/sage/groups/perm_gps/permgroup.py	90.56% <ø> (-0.49%)	⬇️
src/sage/tests/gap_packages.py	94.59% <ø> (ø)
src/sage/env.py	88.05% <100.00%> (+0.05%)	⬆️
... and 57 more

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[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 5f9d256

[collares]

Rebased to match #35093. The CI test failure (log below) seems unrelated:

sage -t --random-seed=101871368592826382261112102728642599044 doc/de/a_tour_of_sage/index.rst
**********************************************************************
File "doc/de/a_tour_of_sage/index.rst", line 66, in doc.de.a_tour_of_sage.index
Failed example:
    integrate(sqrt(x)*sqrt(1+x), x)
Expected:
    1/4*((x + 1)^(3/2)/x^(3/2) + sqrt(x + 1)/sqrt(x))/((x + 1)^2/x^2 - 2*(x + 1)/x + 1) - 1/8*log(sqrt(x + 1)/sqrt(x) + 1) + 1/8*log(sqrt(x + 1)/sqrt(x) - 1)
Got:
    // Giac share root-directory:/sage/local/share/giac/
    // Giac share root-directory:/sage/local/share/giac/
    Added 0 synonyms
    1/4*(2*x - 3)*sqrt(x + 1)*sqrt(x) + sqrt(x + 1)*sqrt(x) + 1/4*log(sqrt(x + 1) - sqrt(x))
**********************************************************************
1 item had failures:
   1 of  32 in doc.de.a_tour_of_sage.index
    [22 tests, 1 failure, 3.30 s]

[dimpase]

lgtm