Update `generate_makefile` to produce sensible error message in all exceptional situations, instead of just some of them. These may surface as one of the first things to someone getting started with the repo.
Bumping some `std` imports to explicitly include the prefix. Also add explicit `./` prefix for local directory imports.
CI: use both cores on GitHub Actions and set timeouts for the local testnet tests
Etan Kissling
Ștefan Talpalaru