Wanted: Smarter recent-messages data/detection

[dgw]

Spawned from #2320, #2327 tries to make an incremental improvement to the way Sopel keeps track of recent messages. This issue exists to take that even further.

As @Exirel said in #2320 (comment):

Albeit not perfect, the time window has it uses as it prevents some false positive. However, it's not really well done, because it only check if the last message is within that time window, so you could have one message 5s away, and the previous 7 a day old, and it'll still think there is a loop.

The relevant code has changed a little and the exact numbers can be configured now, but the sentiment is still true. We talked about improving the data structure, about limiting it in a smarter way (other than just a line count), and about making the repetition detection itself smarter based on those improvements.

Does this need to block 8.0? No, and I won't assign it to that milestone. We just want to keep this in mind for the following release.

[dgw]

Came up again today in chat and I was inspired to do a little research. Behold the TimeDeque object: https://stackoverflow.com/a/75972239/5991