Function payload_io_stats 

pub fn payload_io_stats<T>(payload: &T) -> Result<PayloadIoStats, CuError>
where
    T: Encode,

Measures payload bytes using the same encode path Copper uses for logging/export.

resident_bytes is the payload’s in-memory fixed footprint plus any handle-backed dynamic storage reported during encoding. encoded_bytes is the exact bincode payload size.