hof/tests: use Dagger for hof/mod tests and maybe all testscript base tests

[verdverm]

benefits:

• ephemeral environment, no need to have the dir complexity of testscript currently
• secret management
• consistency between local & actions

Maybe we modify testscript or use our internal HLS runner? HLS might be better because it operates on the real filesystem, so we are testing closer to the real thing