Proxypatternpool

Improve semaphore stats output, str() was useless.

Improve observability and reduce LoC.

Rework internals to reduce lock time.

- add `delay` parameter for forcing house keeping round delays.
- add health check hook.
- rework and improve statistics.
- improve documentation.
- drop `close` and `max_delay` upward compatibility parameters.

Show run time in stats.

Generate stats.