Adds pl-apply-goal helper for safe call/N goal construction (atom or compound),
five solver helpers (pl-solve-forall!, pl-solve-maplist2!, pl-solve-maplist3!,
pl-solve-include!, pl-solve-exclude!), five cond clauses in pl-solve!, and a
new test suite (15/15 passing). Total conformance: 390/390.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>