Improve or remove MessageSplit feature

[soliton-]

Is your feature request related to a problem? Please describe.
Messages can be split multiple times when sent to IRC.
Message splitting is done in girc since lrstanley/girc@658eba5.
Also there is the MessageSplit feature to do the splitting in matterbridge.

Describe the solution you'd like
IMO ideal would be to get message splitting with repeating the bridged nick (which presumably girc cannot do) and some indication that splitting was done (possible via MessageClipped in matterbridge though a bit awkwardly used for splitting and clipping) which girc currently does not do as far as I could see.

Describe alternatives you've considered
Since it's difficult for matterbridge to do the splitting correctly and the feature was probably only added because girc didn't have it at the time, removing the splitting in matterbridge might be the more realistic option.

Another aspect mentioned on IRC is that IRCv3 Multiline will obsolete the need for splitting.

Additional context
Example of the double splitting: https://irclogs.wesnoth.org/2026/03/%23wesnoth.2026-03-12.log at 13:52:49

[poVoq]

Sorry for the late response, somehow I thought we already discussed this? Maybe in the chat?

Would you be able to make a PR for removing message splitting from the IRC bridge?

I agree that if girc is now handling that, it is better to simplify our code and hopefully IRCv3 multiline will just start working when girc completes the implementation of that.