datalog: semi-naive saturator + delta sets (Phase 5, 114/114)

dl-saturate! is now semi-naive: tracks a per-relation delta dict,
and on each iteration walks every positive body-literal position,
substituting the delta of its relation while joining the rest
against the previous-iteration DB. Candidates are collected before
mutating the DB so the "full" sides see a consistent snapshot.
Rules with no positive body literal (e.g. (p X) :- (= X 5).)
fall back to a one-shot naive pass via dl-collect-rule-candidates.

dl-saturate-naive! retained as the reference implementation; 8
differential tests compare per-relation tuple counts on every
recursive program. Switched dl-tuple-member? to indexed iteration
instead of recursive rest (eliminates per-step list copy). Larger
chains under bundled conformance trip O(n) membership × CPU
sharing — added a Blocker to swap relations to hash-set membership.

lib/datalog/conformance.conf

@@ -18,4 +18,5 @@ SUITES=(
   "unify:lib/datalog/tests/unify.sx:(dl-unify-tests-run!)"
   "eval:lib/datalog/tests/eval.sx:(dl-eval-tests-run!)"
   "builtins:lib/datalog/tests/builtins.sx:(dl-builtins-tests-run!)"
+  "semi_naive:lib/datalog/tests/semi_naive.sx:(dl-semi-naive-tests-run!)"
 )