Previously, metadata foo bar baz = 23 was accepted, but according to the definition https://smithy.io/2.0/spec/idl.html#grammar-token-smithy-MetadataSection it should be "metadata"<whitespace>Identifier/String<optional whitespace>.
This triggers a new case in the HtmlFormatter, which emits an empty span at the end of the line for a new line, as those are removed by the split-by-parts code. This requires separate post-processing. Doesn't fix all whitespace issues with Python either, but we're done to 360 failing examples with that, from previously >400.