js-on-sx: JS functions accept extra args silently

SX strictly arity-checks lambdas; JS allows passing more args than
declared (extras accessible via arguments). Was raising "f expects
1 args, got 2" whenever Array.from passed (value, index) to a
1-arg mapFn. Fixed in js-build-param-list: every JS param list
now ends with &rest __extra_args__ unless an explicit rest is
present, so extras are silently absorbed.
conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -56,6 +56,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 146.9,
+  "elapsed_seconds": 154.6,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,7 +1,7 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 146.9s
+Wall time: 154.6s
 
 **Total:** 80/99 runnable passed (80.8%). Raw: pass=80 fail=13 skip=1 timeout=6 total=100.
 

lib/js/transpile.sx

@@ -930,7 +930,7 @@
   (fn
     (params)
     (cond
-      ((empty? params) (list))
+      ((empty? params) (list (js-sym "&rest") (js-sym "__extra_args__")))
       ((and (list? (first params)) (js-tag? (first params) "js-rest"))
         (list (js-sym "&rest") (js-sym (nth (first params) 1))))
       (else