Remove test only distinction for group_context_ext_proposal

[cameronvoell]

This is related to libxmtp Mutable Metadata:

• Mutable Metadata (name a group) libxmtp#548
• Mutable Metadata via new UpdateMetadata intent kind libxmtp#603
• Add group mutable metadata for group names proto#158

[neekolas]

Thanks. I need this for some work I have coming up too

[neekolas]

The CI for this repo is very fussy about having documentation on any public method, so changing the visibility requires more docs.

[keks]

This looks like it should to the trick, looks good! I just have one very minor stylistic note, but feel free to ignore that :)

[keks]

This is really just a stylistic nitpick, but I'd suggest merging this line back into the use super::{...} block below, otherwise it looks like there was a crate called "core_group".

If you need the core_group binding later, you an do

use super::{
  core_group::{self, create_commit_params::CreateCommitParams},
  // ...
}

[cameronvoell]

thanks fixed here 7395004