Function yyjson_val_mut_copy 

pub unsafe extern "C" fn yyjson_val_mut_copy(
    doc: *mut yyjson_mut_doc,
    val: *mut yyjson_val,
) -> *mut yyjson_mut_val

Copies and returns a new mutable value from input, returns NULL on error. This makes a deep-copy on the immutable value. The memory was managed by mutable document. @note imut_val -> mut_val.