Gives HistoryDb an in-memory mode and reconcile() an injectable
deployments list so HistoryService can be exercised hermetically,
without touching the real history.db or shelling out to rpm-ostree.
Covers bootstrap, idempotent reconcile, install-then-reboot,
manual/detected changes, last_known_safe, and chain walking.
Also fixes the pre-existing widget boot-smoke test: startup now makes
a second real Process.run call (via HistoryService.reconcile), which
tipped flutter_test's fake-time zone into flagging a dangling Timer
from that real I/O. Wrapping the pump in tester.runAsync() is the
standard fix.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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