Refactor Syntactic Warnings

[gabegma]

Part of #383

Description:

First pass at refactoring dataset warnings to eventually allow them to run on just one dataset split.

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[JosephMarinier]

I think we can simplify a couple of loops by using of .items() instead of .keys(). In fact, it's quite rare that we need .keys(), we almost always also need the values.

[JosephMarinier]

What a breath of fresh air! Good job!
I only had some small comments about cosmetic changes, for readability. The architecture and the logic look perfect! 👍