Cache compiled source code to speed up deployment

[neuromancer]

Compiling all the engines takes a long time, so it is recommended to cache the compiled artifacts in the github action so it will only recompile the one ones. I already drafted a PR for adding cache: #7 but I need to have the workflow approved to test it.

[chkuendig]

I'll close this and delete it later since it's a duplicate of the PR.

[chkuendig]

Reopen as the cache didn't work for me. I'll look into this again.