Speed up RandomIsomorphismTestUEM

[hulpke]

by pre-filtering candidate generator sets for H using few random word orders before computing Size(Group(gens2)). The few random word orders are computed once for gens1 and reused each iteration, discarding mismatched gens2 cheaply.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.08%. Comparing base (d1e02a6) to head (b78a62e).

Files with missing lines	Patch %	Lines
gap/upext.gi	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
- Coverage   64.20%   64.08%   -0.12%     
==========================================
  Files          12       12              
  Lines        2165     2169       +4     
==========================================
  Hits         1390     1390              
- Misses        775      779       +4     

Files with missing lines	Coverage Δ
gap/upext.gi	64.58% <0.00%> (-0.78%)	⬇️

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