js-on-sx: arrays inherit from Array.prototype on lookup miss

js-get-prop for SX lists fell through to js-undefined for any key
not in its hardcoded method list, so Array.prototype.myprop and
Object.prototype.hasOwnProperty were invisible to arrays.
Switched the fallback to walk Array.prototype via js-dict-get-walk,
which already chains to Object.prototype.
built-ins/Array: 14/45 → 16/45. conformance.sh: 148/148.

lib/js/test262-scoreboard.md

@@ -1,30 +1,24 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 132.0s
+Wall time: 71.8s
 
-**Total:** 14/45 runnable passed (31.1%). Raw: pass=14 fail=25 skip=5 timeout=6 total=50.
+**Total:** 43/50 runnable passed (86.0%). Raw: pass=43 fail=4 skip=0 timeout=3 total=50.
 
 ## Top failure modes
 
-- **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}\
+- **4x** Test262Error (assertion failed)
+- **3x** Timeout
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Array | 14 | 25 | 5 | 6 | 50 | 31.1% |
+| built-ins/Number | 43 | 4 | 0 | 3 | 50 | 86.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Array  (14/45 — 31.1%)
+### built-ins/Number  (43/50 — 86.0%)
 
-- **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}\
+- **4x** Test262Error (assertion failed)
+- **3x** Timeout