Mention suggestion persists even after you continue typing

Observed behaviour

This is a revised version of #1963 The mention suggestions persists there and blocks other things such as emote suggestions. Note this doesn't happen in DMs or personal notes.

Reproduction steps

Start typing a message
Put a @ character to bring up the mention suggestions
Put any letter directly after the @
Put a space then keep typing

Build information

Version 1.0.0, Beta 49, Channel Beta, Build 55, iOS 26.6 (arm64), Device iPhone13,1, Locale en-GB, Push apns, Flutter 3.44.9, Dart 3.12.2

Platform

iOS

Details

Expected behaviour The mention suggestions should close when no suggestions are found and a space is added