Function encode_monitor_data_response_delta 

pub fn encode_monitor_data_response_delta(
    ioid: u32,
    subcmd: u8,
    prev_value: &NtPayload,
    next_value: &NtPayload,
    filtered_desc: &StructureDesc,
    version: u8,
    is_be: bool,
) -> Option<Vec<u8>>

Encode a sparse monitor-data response containing only fields that changed between prev_value and next_value (projected onto filtered_desc). Returns None when nothing changed — the caller should suppress the send entirely and NOT decrement any pipeline credit.