Parallelize smoketests

[bfops]

Our smoketests take a while to run.

We'd like to parallelize them by spinning up multiple SpacetimeDB instances, isolated by running on separate ports and with separate data directories, and have smoketests running in parallel against them.

[jdetter]

This would be beneficial for both the linux + windows smoketests so I think this is reasonably high priority. The windows smoketests right now are taking sometimes like 50 minutes to complete which is wayyy too long.