Minor improvements to solution enumeration

[fwesselm]

Pre-allocate data structures for solution enumeration. (These changes do not affect behavior.)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.33%. Comparing base (eedc74e) to head (b213563).
⚠️ Report is 5 commits behind head on latest.

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2724      +/-   ##
==========================================
- Coverage   81.33%   81.33%   -0.01%     
==========================================
  Files         349      349              
  Lines       86135    86134       -1     
==========================================
- Hits        70054    70053       -1     
  Misses      16081    16081              

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[jajhall]

Fine by me