erlang: lists keylist BIFs (keyfind/keymember/keydelete/keyreplace/keystore/keytake/keysort) (809/809)

Adds the tuple-keyed list family to lib/erlang/lists-ext.sx: act on
first match, key compare via == (er-equal?), non-tuples/short tuples
pass through. keysort/2 reuses the stable merge sort + full term
order. keytake/3 returns {value, Tuple, Rest} | false. All seven
registered through the er-register-builtin-bifs! wrapper so they
survive mid-run registry resets. lists_ext suite 17 -> 38.

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

lib/erlang/scoreboard.md

@@ -1,6 +1,6 @@
 # Erlang-on-SX Scoreboard
 
-**Total: 788 / 788 tests passing**
+**Total: 809 / 809 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -16,7 +16,7 @@
 | ✅ | ffi | 37 | 37 |
 | ✅ | vm | 78 | 78 |
 | ✅ | send_after | 10 | 10 |
-| ✅ | lists_ext | 17 | 17 |
+| ✅ | lists_ext | 38 | 38 |
 
 
 Generated by `lib/erlang/conformance.sh`.