Function moq_client_set_backend 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn moq_client_set_backend(
    client: u32,
    backend: *const c_char,
    backend_len: usize,
) -> i32

Choose the QUIC backend: "quinn", "quiche", or "noq".

Defaults to whichever is compiled in, preferring quinn. A NULL or empty value restores that auto-detection.

Returns zero on success, or a negative code if the handle is unknown or the backend is unrecognized (which includes a backend this build was compiled without).

Safety

• The caller must ensure that backend is NULL or a valid pointer to backend_len bytes.