All args for Toolchain subclasses now mandatory with release of v2025.1

With [this change](https://github.com/inducer/codepy/blame/3a0492ee2f29e325a28ea8aa049714a873d10649/codepy/toolchain.py#L55) (repeated for each class in the file), bundled in the most recent PyPi release, it appears that all args for instantiating subclasses of `Toolchain` are now mandatory which has forced us to fix our dependencies on a previous release and burn a new version.

I believe `@dataclass(frozen=True, kw_only=True)` would fix this issue.