Adding toBuilder() method on GuildChannel

[doEggi]

Description

I created and implemented the toBuilder method on GuildChannel and all its variants. This way you can "clone" a channel of a guild without copying the data manually. Also you can use an existing channel as a template for new channels.

Connected issues & other potential problems

https://github.com/nyxx-discord/nyxx_extensions/issues/38#issuecomment-2198307221 PS: I don't know how to tag an issue of another repo :(

Type of change

• [ -] New feature (non-breaking change which adds functionality)

Checklist:

• [ -] Ran dart analyze or make analyze and fixed all issues
• [ -] Ran dart format --set-exit-if-changed -l 160 ./lib or make format and fixed all issues
• [ -] I have performed a self-review of my own code
• [ -] I have commented my code, particularly in hard-to-understand areas

Todo:

• [ ] I have made corresponding changes to the documentation

[MCausc78]

This probably should be in nyxx_extensions

[Rapougnac]

As MCaus already said, the scope of this PR is beyond nyxx. This should be in nyxx_extensions instead.