This is primarily a cosmetic change.
- Increases code clarity because all system test blocks now start with `switch_to_system`
- Optimizes dependency ordering because `switch_to_system` has no
dependency on the server sshd
Advantages:
- Pure test evaluations
- The test framework can now be used by flakes that extend nix-bitcoin
- Most features of `run-tests.sh` are now accessible via `nix build`/`nix run`.
We keep `run-tests.sh` for advanced features like `scenarioOverridesFile` and adhoc scenarios.
Other changes:
- `run-tests.sh` now builds aggregate VM tests like `basic` or
`buildable` by creating all VMs in a single evaluation.
This speeds up the tests and eases debugging by separating the eval and build steps.
- Use the new `nix` CLI which has improved build output logging
by prefixing output lines with the origin drv name.
Avoid adding flake resource paths to the store (via string
interpolation).
This reduces performance and can lead to modules getting imported
twice, once through a local path and once through a store path.
This might not be needed in a future Nix release, in which case we can
revert this.
