Changes to do in online change

[ghaith]

Collecting issues that we should still do on online change:

Unwrapping std::sync::Mutex::into_inner does not seem very safe to me - but as you said, since this is hidden behind a feature flag, we can leave it in for now.

Originally posted by @mhasel in https://github.com/PLC-lang/rusty/pull/1319#discussion_r1782644127

Handle the FIXME: comments