go sdk and engine dependency cycle

[spare snow]

having the engine depend on dagger.io/dagger causes an additional problem where we can't bump our buildkit dependency beyond the version in dagger.io/dagger => github.com/dagger/dagger => github.com/moby/buildkit

i'm really considering breaking this cycle by just having another codegen'd package for our tests and CLI to use

another reason: there are some things in the engine that I'd like to test against, but don't want to expose in the Go SDK (e.g. disabling host read/write access)

[spare snow]

i worked around this in my PR by adding another replace rule, but that bubbles all the way up to the SDK: https://github.com/dagger/dagger/pull/3560#discussion_r1007077583

when Docker ships a proper semver version and buildkit adopts it, we'd be able to remove the replace github.com/docker/docker rule, but so long as we have this cycle we'd still need the replace github.com/moby/buildkit rule I added above until we make the engine completely external