CPU usage is misreported.

Currently "0 CPU" means "no CPU metric received in the previous ProfileEvents packet". But there can be many ProfileEvents packets and only a few with CPU increment.

That's why the CPU metric shows something weird like:
```
0
0
0
0
0
1234
0
0
0
...
```

This is unbearable, and the CPU metric should be either fixed or removed altogether.
{
    Packet packet = connection->receivePacket();
    switch (packet.type)
    {
        case Protocol::Server::PartUUIDs:
            return true;
        case Protocol::Server::Data:
            if (!cancelled_)
                onData(packet.block, parsed_query);
            return true;
        case Protocol::Server::Progress:
            onProgress(packet.progress);