Add support for intentionally empty tags

[alliern]

Some scenarios involving intentionally blank tags were resulting in mismatched HTML, after being diffed, like a LaTex span followed by a writing blank span that is then replaced by a second LaTex span. This branch adds support for tags that are intentionally left empty by treating them as unified "words" to be diffed as a whole.

It also adds an optional compare_tag_attributes argument to be used in the same_tag? method on the Operations class. Previously, tags with the same name and different attributes were always treated as "equal" when being diffed, resulting in unpredictable outcomes when, for example, a writing blank span is replaced by a latex span', or an embedded image is replaced by a different image (where the only tag difference is the src attribute). Optionally passing incompare_tag_attributes` allows us to treat tags with different attributes as entirely different content when necessary.

[danblaker]

I don't think we should merge this until it uses a generic approach, e.g. support for diffing specified attributes, rather than OUR-specific tags.

[pvande]

I know frustratingly little about how this is implemented or how it is being used, so I don't feel confident speaking to whether this is fit for purpose or an ideal approach.

I will note that there is no testing around this change, which we should probably remedy before merging — that will at minimum allow us to refactor things in the future, if a better approach reveals itself.

[danblaker]

@alliern I agree with @pvande that testing is a necessary component of this implementation. Luckily, it's arguably the thing that Claude Code is best at.