Instead of multiple references to an anonymous structure to represent affine coordinates, add an actual `AffineCoordinates` structure.
Also properly handle the neutral element during coordinate conversion and fix mixed addition.
And comptime the small precomputation table for basepoint multiplication.
Functions generated by Fiat-crypto are not prefixed by their description any more. This matches an upstream change.
We can now use a single type for different curves and implementations.
The field type is now generic, so we can properly handle the base field and scalars without code duplication.
Uses verified code generated by fiat-crypto for field arithmetic, and complete formulas to avoid side channels.
There's still plenty of room for optimizations, especially with a fixed base. But this gives us a framework to easily add other similar curves.
