Store action in SchreierTransversal

[kalmarek]

• fix some printing issues
• parametrize SchreierTransversal by the type of action so that it is possible to reconstruct representatives even when op ≠ ^ (i.e. G acts on itself via *)
• use randomized shallowing of Schreier trees (direct-product benchmark is now 3×faster)
• update benchmarks timings to new cpu

This is in preparation of kalmarek/SymbolicWedderburn.jl#69

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.48%. Comparing base (e9393ec) to head (68fb486).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   96.42%   97.48%   +1.05%     
==========================================
  Files          11       11              
  Lines         615      635      +20     
==========================================
+ Hits          593      619      +26     
+ Misses         22       16       -6     

Flag	Coverage Δ
unittests	97.48% <100.00%> (+1.05%)	⬆️

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