js-on-sx: arrays accept numeric-string property keys

JS arrays must treat string indices that look like numbers ("0",
"42") as the corresponding integer slot. js-get-prop and js-list-set!
only handled numeric key, falling through to undefined / no-op for
string keys. Added a (and (string-typed key) (numeric? key)) clause
that converts via js-string-to-number and recurses with the integer
key. built-ins/Array: 13/45 → 14/45. conformance.sh: 148/148.

lib/js/test262-scoreboard.md

@@ -1,28 +1,30 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 486.8s
+Wall time: 132.0s
 
-**Total:** 77/99 runnable passed (77.8%). Raw: pass=77 fail=15 skip=1 timeout=7 total=100.
+**Total:** 14/45 runnable passed (31.1%). Raw: pass=14 fail=25 skip=5 timeout=6 total=50.
 
 ## Top failure modes
 
-- **13x** Test262Error (assertion failed)
-- **7x** Timeout
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
+- **20x** Test262Error (assertion failed)
+- **6x** Timeout
+- **2x** TypeError: not a function
+- **2x** ReferenceError (undefined symbol)
+- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 77 | 15 | 1 | 7 | 100 | 77.8% |
+| built-ins/Array | 14 | 25 | 5 | 6 | 50 | 31.1% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/String  (77/99 — 77.8%)
+### built-ins/Array  (14/45 — 31.1%)
 
-- **13x** Test262Error (assertion failed)
-- **7x** Timeout
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
+- **20x** Test262Error (assertion failed)
+- **6x** Timeout
+- **2x** TypeError: not a function
+- **2x** ReferenceError (undefined symbol)
+- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\