Implement RegisterKeys scan service request to register new keys

[arya2]

Motivation

We want a scan service request for adding new keys to the scanner task.

Possible Design

• Pass cmd_receiver in ScanTask::spawn() down to zebra_scan::scan::start()
• Update RegisterKeys(Vec<()>) to RegisterKey(String) or RegisterKey { key, parsed_keys } (or a vector of them)
• Call try_recv() at the top of the scanner loop, example:

    loop {
        loop {
            let cmd = match cmd_receiver.try_recv() {
                Ok(cmd) => cmd,

                Err(TryRecvError::Empty) => break,
                Err(TryRecvError::Disconnected) => {
                    return Err(eyre!("command channel disconnected"))
                }
            };

            match cmd {
                ScanTaskCommand::RegisterKey(key) => {
                    let Ok(parsed_key) = sapling_key_to_scan_block_keys(&key, network) else {
                        continue;
                    };

                    let mut new_parsed_keys =
                        Arc::try_unwrap(parsed_keys).unwrap_or_else(|arc| (*arc).clone());
                    new_parsed_keys.insert(key.clone(), parsed_key);
                    parsed_keys = Arc::new(new_parsed_keys);
                }

                _ => continue,
            }
        }

        let scanned_height = scan_height_and_store_results(

• Accept a String in the RegisterKey scan service request
• Call cmd_sender.send(ScanTaskCommand::RegisterKey(key))
  • Possibly after decoding/validating the viewing key
• Respond to the service request once the message has been sent to the channel