trust anchors: persist the state and timer

The format of TA store is compatible both ways with old kresd.
Note: it requires the parent commit to work, i.e. new libzscanner.
3 jobs for ta-improve in 5 minutes and 13 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #4069
docker linux amd64
build:linux:amd64

00:01:43

 
  Test
passed #4071
docker linux amd64
deckard:linux:amd64

00:03:29

passed #4070
docker linux amd64
test:linux:amd64

00:02:00