Every binary build measures its dependency installation (apt-get
update, the essential and injected packages, each build-dependency
pass) and its package build (debian/rules build plus binary) into a
timings accumulator; the record manifest stores both as an optional
`timings` field when the run ends, whatever the outcome — a failed
build keeps its partial durations, and a run that died before any
timed command records nothing.
`pkh deb list` shows the two durations as DEPS and BUILD columns,
formatted like the age ("45s", "2m41s", "1h02m"); records predating
the field show dashes. The field is serde-optional, so the manifest
schema stays at 1 and existing records remain discoverable and
forkable.