handle worker failures gracefully (#1038)
* handle failures gracefully
* fix super-subtle race condition
* address feedback: panic instead of fatal log and make vars into consts
* pass the frankenphp context to worker-ready function
* reset backoff and failures on normal restart
* update docs
* add test and fix race condition
* fail sometimes but do not be pathological about it
* Use title case
Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>
* fix code style in php
* define lifecycle metrics
* ensure we update unregister the metrics and fix tests
* update caddy tests and fix typo
* update docs
* no need for this
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Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>
