Initial load answer section only if in viewport

As described in #309 (closed) documents with many cuts currently cause 403 responses, most likely due to rate-limiting. In any case, it's unnecessary for the client to load all cuts at once. This change only requests a cut once it is (or is almost) in the viewport. I did some basic testing (used the mantine branch to test against):

• NumCS document with lazy loading
• NumCS document without lazy loading

Another possibility would be to just batch all cuts and load them in a single request.

Closes #309 (closed)