Function store_get_version 

pub unsafe extern "C" fn store_get_version(
    context: *mut c_context,
    store: *mut Store,
    callback: get_string_callback,
    user_data: *mut c_void,
) -> err

@brief get the version of a nix store.

If the store doesn’t have a version (like the dummy store), returns an empty string.

@param[out] context Optional, stores error information @param[in] store nix store reference @param[in] callback Called with the version. @param[in] user_data optional, arbitrary data, passed to the callback when it’s called. @see nix_get_string_callback @return error code, NIX_OK on success.