perf: latency dashboard is misleading

The latency dashboard shows connection establishment latency + 1 round trip, and shows the ping latency in the same plot. ICMP Ping doesn't contain the additional 1 round trip, so it makes all other implementations look worse than they actually are.

Not ideal, but maybe a better way to visualize things is to plot measurement results in multiples of the round trip, and subtract the 1 round trip from our measurement results.

The issue does not name files or tests; start by locating the latency dashboard and the code that combines connection-establishment measurements with ping results. Compare the plotted metrics and evaluate the proposed round-trip normalization. Done means the visualization no longer makes other implementations look worse because of the extra round trip.

Written by the indexing model from the issue text.