StringPtrMap struct
Defined in module std.hashmap (hashmap.l0).
StringPtrMap is an open-addressing hash table with linear probing.
Keys are ARC-managed strings (manual retain/release). Values are caller-managed void pointers.
Struct-of-arrays layout: states — byte per slot (EMPTY / OCCUPIED / TOMBSTONE) hashes — int per slot (cached hash code) keys — string per slot (ARC-managed) values — void* per slot