fix(runtime): built-ins/Object test262 residue

[proggeramlug]

Summary

Mops up the built-ins/Object test262 residue: 3026/3173 (95.4%) → 3062/3173 (96.5%), +36, zero regressions (verified by diffing the per-test failure set before/after — no test that passed on main regresses).

Root causes (4 shared)

1. Array [[DefineOwnProperty]] skipped non-configurable validation. Object.defineProperty/defineProperties on an array did not run ValidateAndApplyPropertyDescriptor for an existing non-configurable property on two paths:

• the index-accessor branch only rejected a data→accessor conversion, not a get/set change on an already-non-configurable accessor;
• the named (non-index) branch did no validation at all, so redefining a non-configurable arr.prop silently succeeded.

Both now route through the existing validate_nonconfigurable_redefine (which compares accessors by func_ptr, immune to the receiver-rebind clone).

2. Object.freeze/Object.seal on arrays missed elements + named props. mark_all_keys only walks (*obj).keys_array; an array's indices live in the dense element store and its named props in ARRAY_NAMED_PROPS — neither is in keys_array. New mark_all_array_props records the dropped writable/configurable attrs on the side tables (gated by OBJ_FLAG_ARRAY_DESCRIPTORS).

3. Exotic-Error builtin slots defaulted to enumerable. A plain err.message = x is a [[Set]] and must not change attributes, but propertyIsEnumerable/own-key enumeration defaulted Error message/stack to enumerable when no explicit attr entry existed — so Object.defineProperties(obj, errObj) wrongly processed them. New exotic_default_enumerable keeps them non-enumerable.

4. js_dynamic_object_get_property ignored Error expandos. It returned undefined for any Error property outside the five native slots, ignoring defineProperty-installed accessor/data expandos — so defineProperties read each descriptor off an Error properties-bag as undefined and threw Property description must be an object: undefined. It now consults the exotic side tables first.

Files

• object/array_object_ops.rs — array define validation + mark_all_array_props
• object/object_ops_frozen.rs — wire freeze/seal to the array path
• object/exotic_expando.rs — exotic_default_enumerable
• object/object_ops.rs — propertyIsEnumerable exotic default
• value/dynamic_object.rs — Error dynamic-get consults expandos

Validation

test262_subset.py --dir built-ins/Object against tc39/test262 @ 4249661, Node v26.3.0 oracle: pass 3026→3062, runtime-fail 147→111, 0 newly-broken.