Clear messages for guild and channel cache methods

[FasterSpeeding]

Summary

Add clear messages for cache and channel guild methods

Why is this needed?

To ensure the message cache's reliability

Ideal implementation

Should be self evident

Checklist

• I have searched the issue tracker and have made sure it's not a duplicate. If it is a follow up of another issue, I have specified it.

[davfsa]

Maybe we should restructure the message to be more helpful with this. Something I have been think about was changing the config for max_messages to a more helpful max_messages_per_channel. I am not sure how well this would function, but maybe store the messages along with the channel object?