cache build stages

[turadg]

Before

https://github.com/Agoric/agoric-3-proposals/actions/runs/6775971345/job/18416450836

Job	Time
build test images	49.8 min
run test images	2.5 min
Build and push complete image	0.5 min

After
https://github.com/Agoric/agoric-3-proposals/actions/runs/6776139160/job/18416966447

Job	Time
build test images	59.5 min
run test images	3.9 min
Build and push complete image	0.8 min

Slower across the board. I don't know if it's just CI weather or the caching IO slowed things down. It's definitely being written to!

❯ gh api \
  -H "Accept: application/vnd.github+json" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  /repos/agoric/agoric-3-proposals/actions/cache/usage
{
  "full_name": "Agoric/agoric-3-proposals",
  "active_caches_size_in_bytes": 19244682819,
  "active_caches_count": 349
}

Second run with caching enabled

https://github.com/Agoric/agoric-3-proposals/actions/runs/6776896609/job/18419392914

Sadly, it's still running start_to_to.sh. I think the solution may require explicit cache management and invalidation. E.g. don't re-build tests that haven't been touched.

[turadg]

Come back to this now that it builds with bake
docker/bake-action#36 (comment)