What codometer actually measures. It finds the files a run covers, counts their
compressed and uncompressed size, evaluates whatever counters a configuration
declares of its own, and holds every measured metric to the limits written
against it.
One package rather than four. Discovery, size, customization, and limits are
each a handful of files that only ever run together, and none of them imports
another — so the join that a measurement is had to live somewhere, and it lives
here rather than in the command-line host that used to hold it.
