Benchmarks: want summary boxplots generated during CI

[FelixMcFelix]

Currently, criterion generates very nice plots of the distribution of runtimes for all of our benchmarks. This is the right level of detail for honing in on a specific benchmark, e.g., the distribution of times received from FBT probes on rx.

A glance view of processing times in and between families of packets would be useful. Each set of results processed by criterion outputs a list of box-whisker values (tukey.json) and other summary statistics (estimates.json), which makes this data easily available. We're already pulling in plotters as a library via criterion, which may be a useful starting point (as handy as Gnuplot is under other circumstances).