agent: cleanup: naming and logs

- Convert const ints to proper consts
- Don't export them
- Don't log in tests
agent: cleanup: un-export registry methods
agent: cleanup: un-export api methods
agent: cleanup: various tidying-up in log module

- Use blocking quit semantics everywhere (chan chan struct{})
- Un-export log and ringbuffer symbols
- s/logLine/line/g
- s/logSink/linec/g
- Comment wrapping at 80 col
- const-ize containerLogRingBufferSize (10000)
agent: cleanup: un-export container types

- s/container/realContainer/g
- s/Container/container/g
- Explicitly ensure realContainer implements container
- Explicitly ensure fakeContainer implements container
agent: cleanup: normalize logs module log output