erlang: lists flatmap/2 + filtermap/2 + mapfoldl/3 + search/2 (862/862)

Higher-order list ops in lib/erlang/lists-ext.sx. filtermap honours
true/false/{true,V}; mapfoldl returns {Mapped, Acc}; search returns
{value,E}|false. lists_ext suite 83 -> 91.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/erlang/scoreboard.json

@@ -1,7 +1,7 @@
 {
   "language": "erlang",
-  "total_pass": 854,
-  "total": 854,
+  "total_pass": 862,
+  "total": 862,
   "suites": [
     {"name":"tokenize","pass":62,"total":62,"status":"ok"},
     {"name":"parse","pass":52,"total":52,"status":"ok"},
@@ -15,6 +15,6 @@
     {"name":"ffi","pass":37,"total":37,"status":"ok"},
     {"name":"vm","pass":78,"total":78,"status":"ok"},
     {"name":"send_after","pass":10,"total":10,"status":"ok"},
-    {"name":"lists_ext","pass":83,"total":83,"status":"ok"}
+    {"name":"lists_ext","pass":91,"total":91,"status":"ok"}
   ]
 }