Fix description and tests for inherent_method_must_use_added

[pksunkara]

Fixes #674

[obi1kenobi]

Very nice, thank you! 🚀

I really appreciate your work on improving the lints! I'd love to merge any more improvements you find. If you might be interested in some opportunities for improvement deeper than the lints themselves, I'd be happy to suggest some ideas as well.

[pksunkara]

All functions defined within an impl block are called associated functions because they’re associated with the type named after the impl.

From my understanding, by default, associated fn of a type means the ones within inherent impl.

[pksunkara]

If you might be interested in some opportunities for improvement deeper than the lints themselves

Honestly, I am really itching to revamp the whole test system so that it can be used to auto-generate documentation. But I have been holding back because I know it needs to be discussed first.

[obi1kenobi]

All functions defined within an impl block are called associated functions because they’re associated with the type named after the impl.

From my understanding, by default, associated fn of a type means the ones within inherent impl.

I'm not sure — and even if that is the case, it's best to err on the side of clarity. It's better to avoid causing misunderstandings than to be technically correct while confusing users.

Honestly, I am really itching to revamp the whole test system so that it can be used to auto-generate documentation. But I have been holding back because I know it needs to be discussed first.

Neat! I agree it could be better, in a variety of ways. Would you care to open an issue and write down your thoughts on it? I'd love to hear what you'd change, how you'd change it, and what auto-generated documentation would be created as a result!

I'm particularly curious about:

• Whether we can make the revamp be a sequence of small, smooth steps, each of which is easy to review and merge, and leaves the overall system better off than before. This would massively de-risk the transition.
• Whether we can easily add testing of the error message templating, since it's had issues in the past — some of which you've flagged as well.
• Whether we should try to adopt a tool like insta (Consider switching to insta for snapshot testing #634) for managing our snapshot tests, or if it would be too slow or otherwise add too much friction.

Another key thing I strongly care about is making sure to keep the CONTRIBUTING.md doc updated to match how development happens, since otherwise our project wouldn't be very contributor-friendly.