Parallelize test suits

[strokovok]

• Parallelize tests using strategy.matrix
• Fix issue with data race (copy target parts instead of symlinking). target/release and target/debug are not actually concurrency-safe, my bad

[birchmd]

Thanks for looking into this! I think this is definitely a step in the right direction!

[birchmd]

I don't think no-clobber will be good enough because we may want to overwrite some files that are updated sometimes. To be honest I'm not 100% sure on this because I don't know exactly how rust compilation artifacts are represented. Regardless, I think rsync might be a better choice here.

I also think it would be good to update the whole target directory, not just debug and release because there are some other build artifacts we care about in target not under those directories (e.g. solidity build artifacts and wasm build artifacts).

[strokovok]

I've came to the exactly same conclusion.
Artifacts in debug in release are suffixed with some hash, so I assumed that compiler kinda only creates artifacts with new hash instead of overwriting existing ones. But it seems to me that it's not true, because cleaning build-cache and starting from scratch gives the same time result :(

So this new solution doesn't help at all, you are right. I'll delete it.
I'm now thinking about implementing the same thing that we had in actions/cache, but saving cache locally, and without using compression. I'll do this in another commit. Thanks for details!

[birchmd]

It's not obvious to me that this will be faster because even though they are now running in parallel, they are also now building from scratch. But it probably doesn't hurt and I assume you'll bring in a new caching solution in a new PR.

Please also merge in develop and revert my needs change since it will not be needed now without the caching.