Don't run tests in parallel.

It makes my laptop cry.
SML test works!
Apparently the VB.NET test always worked. It was the stupid parallel-execution bug that was making it fail, before.
Add Rust test.

I can't run this locally, since my Fedora VM is i686 and rust is
apparently x86-64 only, so I don't know if it works or not.
Fix C# test.
Bump Clojure runTimeout so it works in `sandbox`.