Function read_last_value_for_key 

pub async fn read_last_value_for_key(
    bootstrap: &str,
    topic: &str,
    key: &[u8],
    security: Option<ClientSecurity>,
) -> Result<Option<Vec<u8>>, String>

Return the value bytes of the last record whose key equals key.

If key is empty, returns the last record overall regardless of key.

Errors

Returns an error when configuration is invalid, protocol encoding fails, the broker rejects the request, or transport I/O fails.