Function encode_connection_validation_client_anon 

pub fn encode_connection_validation_client_anon(
    buffer_size: u32,
    introspection_registry_size: u16,
    qos: u16,
    method: &str,
    is_be: bool,
) -> Vec<u8> 

Encode just the payload of a client->server CONNECTION_VALIDATION message with no trailing credentials structure (e.g. “anonymous” auth). Returns payload bytes only (no PVA header).