Treat non-deterministic prep errors as internal errors (#4364)
Closes https://github.com/paritytech/polkadot/issues/4293 This PR changes the way how we treat a certain subset of PVF preparation errors. Specifically, now only the deterministic errors are treated as invalid candidates. That is, the errors that are easily attributable to either the the PVF contents or the wasmtime code, but not e.g. I/O errors that could be triggered by the OS (insufficient memory, disk failure, too much load, etc). The latter are treated as internal errors and thus do not trigger the disputes.