feat(guild, channel): implement new helper methods

[EdVraz]

Checklist

• I've ran pre-commit to format and lint the change(s) made.
• I've checked to make sure the change(s) work on 3.8.6 and higher.
• This fixes/solves an Issue.
  • (If existent): resolves [REQUEST] implement channel invite and channel.get classmethod  #599
• I've made this pull request for/as: (check all that apply)
  • Documentation
  • Breaking change
  • New feature/enhancement
  • Bugfix

[EdVraz]

keeping this as draft until other PRs of me are merged since they're all from the same base branch bruh

[i0bs]

Do we need the get classmethods if we're eventually going for a dynamic solution in the client?

[EdVraz]

Well, we don't "need" them but I figured it would be nice if they existed atleast until that method

[i0bs]

My feelings on the existence of get being here is similar to #470 in which we want a more dynamic solution to it without having to hardcode it per data model, as well as it'll be done when it's addressed.

[EdVraz]

The get methods are removed; merge conflicts corrected