js-on-sx: js-num-from-string uses pow (float) for exponent

js-pow-int 10 20 overflows int64 (10^20 > 2^63), so numeric literals
like 1e20 and 100000000000000000000 were parsing as
-1457092405402533888. The pow primitive uses float-domain
exponentiation and produces 1e+20 correctly. Single call swap in
js-num-from-string. built-ins/String (with --restart-every 1):
67/99 → 70/99. conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -1,9 +1,9 @@
 {
   "totals": {
     "pass": 67,
-    "fail": 19,
+    "fail": 26,
     "skip": 1,
-    "timeout": 13,
+    "timeout": 6,
     "total": 100,
     "runnable": 99,
     "pass_rate": 67.7
@@ -13,18 +13,22 @@
       "category": "built-ins/String",
       "total": 100,
       "pass": 67,
-      "fail": 19,
+      "fail": 26,
       "skip": 1,
-      "timeout": 13,
+      "timeout": 6,
       "pass_rate": 67.7,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          15
+          14
+        ],
+        [
+          "TypeError: not a function",
+          8
         ],
         [
           "Timeout",
-          13
+          6
         ],
         [
           "Unhandled: Not callable: \\\\\\",
@@ -33,10 +37,6 @@
         [
           "ReferenceError (undefined symbol)",
           1
-        ],
-        [
-          "SyntaxError (parse/unsupported syntax)",
-          1
         ]
       ]
     }
@@ -44,11 +44,15 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      15
+      14
+    ],
+    [
+      "TypeError: not a function",
+      8
     ],
     [
       "Timeout",
-      13
+      6
     ],
     [
       "Unhandled: Not callable: \\\\\\",
@@ -64,6 +68,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 580.2,
+  "elapsed_seconds": 364.7,
   "workers": 1
 }