Detecting fast-message spam

Seems like a very basic feature. However, I can't find any way to enable something like this.

Start by reviewing the bot's existing moderation and automoderation entry points to determine where message-rate checks and configuration are handled. The issue names no files or tests, so first establish the intended definition of fast-message spam and how users should enable it; done should include detection and a documented activation path.

Written by the indexing model from the issue text.