feat: add lint struct_with_no_pub_fields_changed

[CommanderStorm]

This draft is mostly to prevent others thinking that nobody is working on this issue.

The query is mostly from struct_with_pub_fields_changed

There is still some tinkering I need to do with

• review the wording of the description => feat: add lint struct_with_no_pub_fields_changed #962 (comment)
• review that the whitness actually generates correct code
• I need to self review. Learning from the semi-desaster in test: migrate the remaining snapshot-test to insta #951, I am going to do that tomorrow though.
• See if I can fix the false-negative for PubStructWithNonPubDocFieldChangedToUnion or mark it as TODO => feat: add lint struct_with_no_pub_fields_changed #962 (comment)

Resolves one checkbox of #954

[CommanderStorm]

(idk if you get notifications for this, assuming you don't)

@obi1kenobi I have reviewed this as thoroughly as possible. Except for the comments above I have not found anything. => I think this is ready for review

[obi1kenobi]

Nice work! Especially good job with the query logic, it was trickier than I thought it would be.

There are a handful of remaining items that require another pass before we can merge. Most of them are the kinds of things that would be good to practice catching in your self-reviews: the top difference between a junior engineer and a senior engineer is whether one independently finds the issues in one's own code, or whether someone else has to point them out. So let's work on it together!

[obi1kenobi]

Looks good modulo a small bug in the witness hint. If you can regenerate the witness file with the fix, this should be good to merge!

[obi1kenobi]

Awesome, nicely done 🚀