make interpreter's Conjunction a Compound node

[quentin]

Conjunctions with hundreds of terms would otherwise overflow the engine stack with left/right recursion.
The issue has been observed in Debug build with ~200 terms.

[codecov]

Codecov Report

Merging #2459 (bba07d6) into master (f766700) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2459      +/-   ##
==========================================
- Coverage   78.20%   78.15%   -0.05%     
==========================================
  Files         486      486              
  Lines       32379    32394      +15     
==========================================
- Hits        25322    25318       -4     
- Misses       7057     7076      +19     

Files	Coverage Δ
src/interpreter/Engine.cpp	85.21% <100.00%> (+0.04%)	⬆️
src/interpreter/Generator.cpp	95.20% <100.00%> (+0.09%)	⬆️
src/interpreter/Node.h	96.96% <ø> (ø)

... and 4 files with indirect coverage changes