datalog: magic-sets building blocks (199/199)

Adds the primitives a future magic-sets rewriter will compose:

  dl-magic-rel-name rel adornment    → "magic_<rel>^<adornment>"
  dl-magic-lit rel adn bound-args    → magic literal as SX list
  dl-bound-args lit adornment        → bound-position arg values

Rewriter algorithm (worklist over (rel, adornment) pairs,
generating seed, propagation, and adorned-rule outputs) is still
TODO — these helpers are inspection-only for now.

4 new magic tests cover naming, lit construction, and bound-args
extraction (mixed/free).

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 194,
+  "total_passed": 199,
   "total_failed": 0,
-  "total": 194,
+  "total": 199,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,8 +13,8 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":18,"failed":0,"total":18},
     {"name":"api","passed":14,"failed":0,"total":14},
-    {"name":"magic","passed":10,"failed":0,"total":10},
+    {"name":"magic","passed":15,"failed":0,"total":15},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T09:50:50+00:00"
+  "generated": "2026-05-08T09:53:23+00:00"
 }