[proggeramlug]

Closes #3148. Follow-up to PR #2499.

Wires the remaining %TypedArray%.prototype methods and instanceof for all typed-array kinds. reduce/reduceRight/copyWithin/findIndex/set already landed on main independently; this fills in the rest by routing typed-array receivers through the generic js_array_* helpers, which delegate to element-typed js_typed_array_* impls via lookup_typed_array_kind.

What's added

Runtime (typedarray.rs) — js_typed_array_join / join_value / slice / reverse / fill / subarray. slice/subarray return a same-kind TypedArray.

Delegation guards

• js_array_reverse / js_array_fill / js_array_fill_range (concat_reverse.rs)
• js_array_slice (splice_slice.rs)
• js_array_join (iter_methods.rs)
• js_array_copy_within (immutable.rs) — this path was previously unguarded; broadening is_array_expr routes TA receivers through it, so the guard is required to avoid reading the element-typed buffer as boxed f64
• keys/values/entries iterator objects materialize the TA to a plain array first (iter_object.rs) so iteration yields numbers, not raw f64 bytes

instanceof — reserved per-kind class ids 0xFFFF0030..3A (through BigUint64Array) in codegen, resolved at runtime via class_id_for_kind. x instanceof Int32Array is now true (and false for the wrong kind / non-TA).

Codegen routing — is_array_expr recognizes Named TA receivers so their not-already-folded methods reach lower_array_method (+ new set/subarray arms + extern decls); the local_array_methods slice arm folds TA receivers to ArraySlice.

indexOf / lastIndexOf / includes already delegate (pre-existing, #2457).

Validation

• Byte-matches node --experimental-strip-types for Int32Array and Float64Array across all the above methods + instanceof (test-files/test_gap_typed_array_proto_methods.ts).
• Plain arrays and already-landed TA methods (map/filter/at/with/sort/findLast) verified unaffected — guards only fire for genuine TA pointers.
• cargo fmt clean. perry-runtime suite green (the only failures are pre-existing gc::tests::barrier flakes that pass in isolation; my changes touch no GC code).