Proxypatternpool

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.

Improved stats.
Improved start and housekeeping resilience.

Improved `str` for improving monitoring and debug.