sparse strategies for composite elliptic-curve isogenies

[yyyyx4]

Fixes #34239.

[codecov-commenter]

Codecov Report

Base: 88.58% // Head: 88.58% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (b52a631) compared to base (293dd72).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #34965      +/-   ##
===========================================
- Coverage    88.58%   88.58%   -0.01%     
===========================================
  Files         2140     2140              
  Lines       396961   396964       +3     
===========================================
- Hits        351655   351643      -12     
- Misses       45306    45321      +15     

Impacted Files	Coverage Δ
src/sage/schemes/elliptic_curves/hom_composite.py	91.76% <100.00%> (+0.14%)	⬆️
src/sage/interfaces/qsieve.py	71.30% <0.00%> (-2.61%)	⬇️
src/sage/groups/additive_abelian/qmodnz.py	91.48% <0.00%> (-2.13%)	⬇️
src/sage/cpython/_py2_random.py	74.38% <0.00%> (-1.66%)	⬇️
src/sage/graphs/generators/random.py	91.09% <0.00%> (-1.20%)	⬇️
src/sage/sets/integer_range.py	91.41% <0.00%> (-0.51%)	⬇️
src/sage/graphs/generic_graph.py	89.02% <0.00%> (-0.50%)	⬇️
src/sage/rings/polynomial/ore_polynomial_ring.py	89.40% <0.00%> (-0.43%)	⬇️
src/sage/quadratic_forms/ternary_qf.py	66.92% <0.00%> (-0.39%)	⬇️
src/sage/graphs/graph_plot.py	84.33% <0.00%> (-0.29%)	⬇️
... and 17 more

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[JohnCremona]

LGTM but I think @defeo should look at it too.

[kwankyu]

Otherwise, LGTM.

[github-actions]

Documentation preview for this PR (built with commit 17a5859) is ready! 🎉

[kwankyu]

Thanks.

[kwankyu]

I wonder why _compute_factored_isogeny_prime_power is a hidden function. The docstring is not accessible in the reference manual. But definitely not to do here.

[yyyyx4]

Thanks to both of you for reviewing this!

The function is hidden because of the leading underscore; it's a common Python convention for internal functions.

[kwankyu]

The function is hidden because of the leading underscore; it's a common Python convention for internal functions.

I know. I wondered why it is an internal function. But never mind now. I won't.