reject growable SharedArrayBuffer without hooks

[jdcaperon]

This PR is AI assisted and human reviewed to the limits of the human, feel free to close and I can re-raise as an issue.

In quickjs.c, js_array_buffer_constructor3() allowed growable SharedArrayBuffer construction without SAB allocator hooks.

Context

Growable SharedArrayBuffer construction could succeed on runtimes created with JS_NewRuntime() when the embedder had not installed SharedArrayBuffer allocator hooks.

In that configuration, construction allocated only the initial byteLength, while SharedArrayBuffer.prototype.grow() later assumed the backing store covered maxByteLength and only updated the logical byte length.

That mismatch could let typed array and DataView access reach beyond the native allocation after growth.

Intent

Fail closed during JS-created growable SharedArrayBuffer construction when sab_alloc is unavailable.

Fixed-length SharedArrayBuffer construction remains allowed without hooks. Runtimes that install SAB allocator hooks can still construct and grow SABs backed by the upfront maxByteLength allocation.

The C API regression coverage checks the default-runtime rejection path, preserves fixed-length SAB behavior, and verifies hooked-runtime growth exposes zero-filled bytes beyond the initial length.