Rewrite with newer Zoo APIs and support new Github UI

[pierremtb]

Why?

The way this was written in 2023 both lacks a lot of features that we could enable today with Zoo's stack and isn't compatible anymore with the rollout of Github's new Issue and PR UI. Today this extension only uses file conversions APIs and does all the rendering and diffing locally.

How?

As the need for visual 3D diffs materializes in modeling-app, see KittyCAD/modeling-app#8489, there will be chances to leverage the work done there to enable a more modern and scalable way to achieve the initial goal here of 3D CAD diffs right inside PR reviews, powered by Zoo.

Some initial discussions can be found at https://kittycadworkspace.slack.com/archives/C06D81NS0DR/p1750877512853989

[jacebrowning]

Unlimited usage of the new extension should also be available to Pro plans and above, so we'll have to update billing to reflect that.