Add embedded unittesting framework Change-Id: Ie0b9fb17baba5acde9f491b8b0360005152ddb4a Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/maize/+/256319 Reviewed-by: Travis Geiselbrecht <travisg@google.com> Commit-Queue: Erik Gilling <konkers@google.com> Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>