Message list API: add truthful `has_more` per direction (requires visible-row refill)

(#1359) Feature Under consideration api performance

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Comment by Hampus
HampusStaff 1 vote originally by @hampus-fluxer on GitHub
migrating to a discussion because there's nothing wrong with how it works currently and the web app can handle this perfectly fine, so it's a feature request rather than a bug report