Function blosc2_schunk_open_offset 

pub unsafe extern "C" fn blosc2_schunk_open_offset(
    urlpath: *const c_char,
    offset: i64,
) -> *mut blosc2_schunk

@brief Open an existing super-chunk that is on-disk (frame). No in-memory copy is made.

@param urlpath The file name.

@param offset The frame offset.

@return The new super-chunk. NULL if not found or not in frame format.