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.md

@@ -1,15 +1,15 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 280.3s
+Wall time: 382.7s
 
-**Total:** 73/99 runnable passed (73.7%). Raw: pass=73 fail=20 skip=1 timeout=6 total=100.
+**Total:** 75/99 runnable passed (75.8%). Raw: pass=75 fail=18 skip=1 timeout=6 total=100.
 
 ## Top failure modes
 
 - **10x** Test262Error (assertion failed)
-- **8x** TypeError: not a function
 - **6x** Timeout
+- **6x** TypeError: not a function
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)
 
@@ -17,14 +17,14 @@ Wall time: 280.3s
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 73 | 20 | 1 | 6 | 100 | 73.7% |
+| built-ins/String | 75 | 18 | 1 | 6 | 100 | 75.8% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/String  (73/99 — 73.7%)
+### built-ins/String  (75/99 — 75.8%)
 
 - **10x** Test262Error (assertion failed)
-- **8x** TypeError: not a function
 - **6x** Timeout
+- **6x** TypeError: not a function
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)