js-on-sx: TypeError-on-not-callable uses type-of, not (str fn-val)

Formatting wrapper dicts with (str fn-val) recursively walks the
proto chain through SX inspect — for String/Number wrappers whose
prototype contains lambdas this hangs. Switched the message to
(type-of fn-val), e.g. "dict is not a function". Less specific
but always terminates.
built-ins/String: 73/99 → 75/99 (canonical). conformance.sh:
148/148.

lib/js/test262-scoreboard.json

@@ -1,33 +1,33 @@
 {
   "totals": {
-    "pass": 73,
-    "fail": 20,
+    "pass": 75,
+    "fail": 18,
     "skip": 1,
     "timeout": 6,
     "total": 100,
     "runnable": 99,
-    "pass_rate": 73.7
+    "pass_rate": 75.8
   },
   "categories": [
     {
       "category": "built-ins/String",
       "total": 100,
-      "pass": 73,
-      "fail": 20,
+      "pass": 75,
+      "fail": 18,
       "skip": 1,
       "timeout": 6,
-      "pass_rate": 73.7,
+      "pass_rate": 75.8,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
           10
         ],
         [
-          "TypeError: not a function",
-          8
+          "Timeout",
+          6
         ],
         [
-          "Timeout",
+          "TypeError: not a function",
           6
         ],
         [
@@ -47,11 +47,11 @@
       10
     ],
     [
-      "TypeError: not a function",
-      8
+      "Timeout",
+      6
     ],
     [
-      "Timeout",
+      "TypeError: not a function",
       6
     ],
     [
@@ -64,6 +64,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 280.3,
+  "elapsed_seconds": 382.7,
   "workers": 1
 }