`i in arr` with a non-literal number key boxed the typed array into the
checked-dynamic tree and materialized every element per evaluation, so
`for (...) if (i in arr)` loops were quadratic (1e4 elements: 5.3 s vs
Node 0.7 ms). A number key over an array receiver now lowers to arrayHas
(scr_arr_has), the query the literal fold and Object.hasOwn already use;
the key is stabilized first to keep JS evaluation order.
`k in dict` with a runtime string key over an index-signature record
snapshotted and scanned every overflow key per probe (1e4 keys: 436 ms,
1e5: timeout). The helper now ends in recordOvfHas (scr_map_has_str).
