Current multiline error/notice reporting is hacky, e.g.

Notice how

• we call notice multiple times even as it relates to the same core issue
• we pass allow_dups=True to suppress deduplication of, say, the same type
• we mistakenly(?) dedup the "Superclass:" and "Subclass:" notices
• by always doing allow_dups=False, we can effectively dedup when it would make sense

I think it'll be better if the extra lines could be part of the error, also reducing code duplication (we end up passing a lot of the same parameters multiple times). Is there a reason why we didn't? Is it a pattern elsewhere in the code?