Investigate: usage of resources

[foresterre]

Currently we don't bother trying to use the hosts resources more effectively, if the current is_compatible(Rust version) -> bool check does not have a high resource utilisation (we don't even check for it).

This is based on the idea that the Rust compiler is rather good at (high) resource utilisation. However, this is not always the case. We could consider running some extra is_compatible checks if the hosts resource utilisation allows it.

Risk: doing this well is a hard problem, doing it poorly may even lengthen the runtime instead of shortening it

Side advantage: when we re-add more heuristic / alternative is_compatible check runners; which are a lot faster than running the compiler and tools, then this may become even more useful.