The GHA cache is very slow, taking on the order of minutes to save and
restore from.
Use WarpBuild's cache instead as this is in the same region and much
faster.
WarpBuild cache action does not auto-fallback to GHA if not being run on
Warp. To allow fork runs to fallback to GHA caching, whilst minimising
duplication in the action files, create new "interal" actions which
perform the switching logic, and use these in the (renamed) cache|save
actions.
Without this we would need the `if` logic in our prvious actions, 4
times in each of save and restore.
Plumb the provider through into the action, as a composite action can't
read `env` (`GITHUB_OUTPUT`) from previous steps.
Cirrus is winding down and github now offers more than 10GB cache.
Switch to GH cache for all runner-types. Simplify docker build arg
construction, and reduce the number of needed action permissions.
Instead of enumerating each passed env var, just pass all. This avoids
the risk of missing to enumerate one. Also, it is less code.
The risk could be that an env var causes non-deterministic behavior, but
this can be fixed by explicitly excluding it once the issue is known.
Values with newlines can not be stored in the file and parsed by
docker/podman, so they are excluded.
