[enhancement] replace mentions in user messages with @username form before sending to the ai

[Butterroach]

so the bot can know who users are talking about

for example, replace <@707325473356775536> is stupid with @butterroac is stupid

keep it the same if the user could not be found

[Butterroach]

torture

[hyd3rs]

so the bot can know who users are talking about

for example, replace <@707325473356775536> is stupid with @butterroac is stupid

keep it the same if the user could not be found

marking to add in #74 and in the old legacy system