nx_intern.nx

nx_intern.nx -- string interning pool. Maps a (bytes, len) -> stable i64 id. Same string content always gets the same id; ids are dense from 0. Foundation for: * Symbol table dedup in nxld + nxasm * Identifier interning in lex (turns strcmp into ==) * Section name interning across the .shstrtab + .strtab * Type-name dedup in opt Internally: * nx_hash for FNV-1a key -> id lookup * Backing byte buffer holding the actual string content, each entry NUL-terminated (so nx_intern_at returns a *u8 directly usable as a C-string) * Side-array of (offset, length) pairs indexed by id API: nx_intern_new(bytes_cap, ids_cap) nx_intern_get(t, bytes, len) -- returns id (creates if new) nx_intern_at(t, id, out_len) -- returns *u8 + length nx_intern_count(t) -- total ids assigned Performance: O(1) average for get + at; backing buffer never re-allocates so all returned *u8 stay valid for the table's lifetime (a critical invariant for symbol-table users).