introduce sparse compounds/lists for functor/3 and length/2

[ichiban]

#226

[codecov]

Codecov Report

Base: 99.07% // Head: 99.08% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (a0e5cc7) compared to base (ff2a162).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #277   +/-   ##
=======================================
  Coverage   99.07%   99.08%           
=======================================
  Files          22       22           
  Lines        7282     7359   +77     
=======================================
+ Hits         7215     7292   +77     
  Misses         50       50           
  Partials       17       17           

Impacted Files	Coverage Δ
engine/builtin.go	99.09% <100.00%> (+<0.01%)	⬆️
engine/clause.go	98.41% <100.00%> (+0.01%)	⬆️
engine/compound.go	100.00% <100.00%> (ø)
engine/env.go	98.94% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[ichiban]

closed in favor of a more straightforward solution #279