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.
{
            return std::tie(name, host_name)
                 < std::tie(rhs.name, rhs.host_name);
        }
    };
    std::map<Id, UInt64> rows_by_name;
    for (size_t src_row = 0; src_row < src.rows(); ++src_row)
    {
        Id id{
            src_column_name.getDataAt(src_row),
            src_column_host_name.getDataAt(src_row),
        };
        rows_by_name[id] = src_row;
    }
    /// Filter out snapshots
    std::seer_mask;
    for (size_t i = 0; i < src_array_thread_id.size(); ++i)
    {
        if (src_array_thread_id[i] != 0)
        {
            thread_id_filter_mask.emplace(i);
        }
    }
    /// Merge src into dst.
    for (sizw < dst_rows; ++dst_row)
    {
        Id id{
            dst_column_name.getDataAt(dst_row),