fix(buffer): materialize Buffer iterators via spread + Array.from (#3909)

[proggeramlug]

Summary

buf.keys(), buf.values(), and buf.entries() returned working iterator objects (.next() and for...of produced the right byte indices/values), but [...buf.keys()] and Array.from(buf.values()) returned an empty array.

js_array_clone_for_spread — the runtime helper behind array spread and Array.from — recognizes iterator objects by class id, but its is_array_iterator check listed only the array/map/set/iterator-helper class ids, not BUFFER_ITERATOR_CLASS_ID. A Buffer iterator therefore fell through to the array-like .length/[i] materialization path (which a Buffer iterator doesn't support), yielding nothing. Added the buffer iterator class id alongside the others so spread and Array.from drive its .next() protocol like every other iterator.

Testing

Verified byte-for-byte against node --experimental-strip-types:

[...buf.keys()]            → [0,1,2]
[...buf.values()]          → [byte values]
Array.from(buf.entries())  → [[i,v], …]

.next() and for...of (already working) stay covered. Added node-suite/buffer/iterator-spread regression fixture. Local suites green (perry-runtime, perry-hir), cargo fmt --check clean.

Closes #3909