Avoid building each go module separately

Currently we build each go module separately, in a new separate container. Since we have a lot of go modules, this takes a long time, just for extracting/removing each container.

To make the build faster, we could avoid building anything in each of the go module projects, only creating source tarballs (which does not require using a container), and only do the build in the projects using those modules (snowflake, obfs4, etc ...).