Add some form of CI for Windows

[gregcotten]

Just as the title says. There should be continuous testing on Windows x86_64 and arm64 so that releases don't just break with a BoringSSL bump, etc. Even just a smoke test would be extraordinarily helpful.

[Lukasa]

Thanks @gregcotten. I don't disagree with this in any particular way. Getting this CI setup is on the roadmap, but we're not immediately there. @FranzBusch is driving the CI adoption there.