Refactor subscribers and handle errors better

[davidlougheed]

Description

• Improve performance of subscribers by caching some values in the cog instance
• Avoid creating cog multiple times
• Handle uncaught exceptions from the coroutines
• Reduce repetition using a decorator

Motivation and Context

• Issue [BUG] Need to handle thread crashes in subscribers #236
• Making it easier to make new subscribers

How Has This Been Tested?

• Made sure subscribers still ran

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[jidicula]

1 question about filenaming but otherwise good to merge

[jidicula]

should this file be named differently to avoid confusing its purpose with cogs/subscribers.py?

[le-potate]

Looks good, could be a good idea to catch the exceptions happening in check_metro_status directly too. But this shouldn't crash anymore, and I tested and subscriber.py still works (food recalls were sent)

[davidlougheed]

@le-potate will this conflict at all with the webhook logger stuff?