Struct ZIO 

pub struct ZIO { /* private fields */ }

Buffered input stream wrapping an external chunk-reader callback.

Corresponds to struct Zio / ZIO in lzio.h. The C struct stored a lua_State *L back-pointer and a void *data opaque pointer alongside a raw lua_Reader function pointer. In Rust:

• lua_State *L is removed from the struct; callers hold &mut LuaState directly and pass it to fallible methods (per types.tsv).
• void *data is folded into the reader closure (per types.tsv).
• const char *p (raw pointer into the reader’s internal buffer) becomes a usize index into the owned current_chunk field.

C mapping (types.tsv)

Zio           → ZIO
.n            → usize         (bytes still unread in current_chunk)
.p            → usize         (cursor index; was const char *)
.reader+.data → Box<dyn FnMut() -> Option<Vec<u8>>>  (combined)
.L            → removed; callers pass &mut LuaState to methods

PORT NOTE: The types.tsv entry for Zio.reader lists Box<dyn FnMut() -> Option<&[u8]>>, but &[u8] cannot name a lifetime in a dyn Fn trait object without HRTB and a pinned source. Phase A uses Option<Vec<u8>> instead; the reader returns an owned chunk. Phase B should evaluate whether a zero-copy &[u8] path is achievable (e.g. by making the reader hold a pinned internal buffer and returning a slice into it via HRTB).