Notarization is completely optional when building any OSS software on a Mac, and not part of any default build process I know. A Mac can sign builds for running locally, a process which is fast, completely local, and does require building test binaries or anything like that. Even a Mac building for an iPhone in developer mode has a local cert it can use, and doesn't require notarization.

Notarization is only needed when distributing binaries to others. Personally I do it once a month for the Mac app I distribute.