I think I meant to make these changes over 6 months ago. alas, better
late than never.
1. should_reject doesn't eagerly intern the endpoint string
2. Rate limiter uses a std Mutex instead of a tokio Mutex.
3. Recently I introduced a `-local-proxy` endpoint suffix. I forgot to
add this to normalize.
4. Random but a small cleanup making the ControlPlaneEvent deser
directly to the interned strings.
The overall idea of the PR is to rename a few types to make their
purpose more clear, reduce abstraction where not needed, and move types
to to more better suited modules.