use docker base image in CI

[abe-winter]

What changed

• consume prebuilt base image in test.yml rather than building every time
• split test.yml build + test into separate steps

Why

• intermittent failures of the base image step (example here)
• clearer output (location of build vs test error is clearer)
• slightly quicker

Follow-up work

• scheduled rebuilds of base image

[lia-viam]

for my benefit and posterity can you elaborate/eli5 a bit on consuming the pre-built base image? like where is that image coming from, is it manually uploaded rn or could be scheduled in the future, etc

[abe-winter]

where is that image coming from, is it manually uploaded rn or could be scheduled in the future, etc

the image is created by this job https://github.com/viamrobotics/viam-cpp-sdk/actions/workflows/docker.yml

and it gets uploaded to here https://github.com/viamrobotics/viam-cpp-sdk/pkgs/container/cpp-base/307921886?tag=bullseye-amd64

(if you scroll down on that page, note it embeds the git sha so we have a fairly good idea of where this came from; not sure if the sha is attested by the runner, but they're giving us a blue check on the right side of the page; I think some attestation is happening)

could easily add a cron trigger to docker.yml if we wanted

[abe-winter]

these docker images are also listed on the side of the repo main page if you need to find them in a hurry