Reserve more notation in `integers.v`.

Avoid duplicating details like at level 35.

This is a bit of a slippery slope. (I reserved just the notation that I overload elsewhere.)

I reserved just the notation that I overload elsewhere.

What do you mean by that?

What's the status of this, @robbertkrebbers and @swasey ?

I propose we close this due to lack of activity. No point in keeping it around. @swasey you can re-open this if you still have a need for it.

closed