... and adds an example builtin which returns the current epoch.
The types introduced by this, especially in the interpreter module,
are going to be used for user-defined functions, too.
Change-Id: I0364a67241e94642cde08489ac711a340e30ebe8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2381
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI