feat(ci): use Hercules CI (#2382)

Moves to Hercules CI for our primary build jobs.
Will move schedules jobs and effects to Hercules in the coming weeks.

Caveats:
- Not all jobs could be migrated
- `site` and any other LFS jobs will still be build on nixbuild / GHA
until LFS support is added to Hercules
- Will still evaluate garnix as they resolve issues
- Only two 16 runner machines currently, I'll scale this up after
incoming changes to the infra repo make it easier to do so