Handling inline comments outside the main verus-body

[parno]

The main parse_and_format has special handling for top-level comments and items, but this means those items don't benefit from/share code with the main formatting logic in to_doc. For example, when we process this code:

verus! {

pub type ReplicaId = usize; // $line_count$Trusted$

} // verus!

It gets parsed as a top-level type_alias item followed by a comment that gets treated as a top-level suffix comment in parse_and_format, which means we don't notice that it's been flagged as an inline comment. We could replicate that logic in parse_and_format, but I suspect we should instead try to simplify parse_and_format and rely more consistently on to_doc.