Faster flag complex

[maximelucas]

Adresses #264

flag_complex and random_flag_complex were computing all maximal cliques and then letting add_simplices_from dealing with the max_order parameter.
This means that a small network with large density was already very long to compute, e.g.

H = xgi.random_flag_complex(50, 0.7)

I changed this: only cliques up to max_order are computed and then passed to add_simplices_from.

%timeit H = xgi.random_flag_complex(50, 0.6, seed=1)
# --> 22.6 s ± 198 ms # before
# --> 269 ms ± 690 µs # now

Roughly a 100x speedup, expected to be more for larger and denser graphs.

I also added some tests because the ones we had were testing consistency but not correctness.

[maximelucas]

(The new commits are the last two, not sure why the others appear here, I think they're from a past PR)

[codecov]

Codecov Report

Patch coverage: 94.44% and project coverage change: -0.04 ⚠️

Comparison is base (a58a4b8) 90.55% compared to head (82d5573) 90.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #355      +/-   ##
==========================================
- Coverage   90.55%   90.51%   -0.04%     
==========================================
  Files          41       41              
  Lines        3016     3025       +9     
==========================================
+ Hits         2731     2738       +7     
- Misses        285      287       +2     

Impacted Files	Coverage Δ
xgi/generators/simplicial_complexes.py	96.77% <94.11%> (+0.30%)	⬆️
xgi/generators/classic.py	97.87% <100.00%> (+0.04%)	⬆️

... and 1 file with indirect coverage changes

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[leotrs]

:)

[maximelucas]

Thanks Leo! Should all be addressed.