Feature/loop for crashed tasks

[rakovskij-stanislav]

Karton already supports debug mode, but sometimes you need to works with already "unwealthy" tasks that crashed.

Restarting them is not an option - you cannot predict which consumer will get this task, while you need to feed this task to exact consumer you run under debugger / with extra prints / etc. The goal is to debug crashed task without interrupting the processing.

This PR introduces new method, Consumer.loop_crached_tasks that gradually makes debugging process more easy by working only with crashed tasks. It has several restrictions:

• It ignores timeouts (for benefit of debugging).
• It works with karton.tasks instead of karton.queue list in redis.
• It does not register new binds, shut down already running instances.
• It does not increment CRASHED metrics on further crashes.
• It does not immediately change this task status to STARTED.