This allows adding more stuff into this namespace, from different files.
Also move tests on proto-related code from src/tests to src/proto/tests.
Change-Id: I49e066fce90efbc18e16d68f94497b32ed5625c0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8091
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI