Attempt to cleanup protobuf usage per the notes in #742. But the big one is that gogo/protobuf is unmaintained/looking for project ownership so revert to Google's protobuf library.

• Remove gogo/protobuf from all sources
• Make all protoc compiler runs consistent and modern:
  • Change the few go generate files using --gofast_out= to the normal compiler
  • Change all go generate to use --go_opt=paths=source_relative flag to keep our invocation/directory layout
  • Change all .proto files to include option go_package = "..."; (compiler fails otherwise)
• Regenerate all protobuf files using modern protoc and protoc-gen-go
• Run tests make test
• Finally, go mod tidy

This needs some reasonable amount of testing to make sure everything works as expected.