Duo Chat is getting slower as the message count increase

Problem

Found in https://gitlab.slack.com/archives/C05CJ1T3P0W/p1738649916648039

Duo Chat is getting slower as the message count increases. It's less likely that this issue occurs on production because it's guarded by the rate limiter in GraphQL Endpoint, however, the internal evaluation endpoint api/v4/chat/completions doesn't have this mechanism and could end up having tons of messages in the same thread.

Proposal

Optimize the message fetching query to avoid the timeout error.