Add: BinaryInteger/ilog(_:)

[oscbyspro]

BinaryInteger/ilog2() is basically a bit counting operation, which is why it returns Count<IX>. This is awkward when you want the result as an instance of Self. Instead of adding a bunch of overloads, I think it might be better to perform this conversion in an arbitrary base function. The latter offers additional utility and a constant binary base argument should fold into a simple conversion, assuming I add an appropriate fast path.

[oscbyspro]

I might need a Radix<T> (natural ≥ 2) type so that Nonzero<T.Magnitude> can return a nonoptional result. Hm. Never-mind. Nonzero<T.Magnitude> may be infinite. I would also need Nonzero<Natural<T.Magnitude>>. Meh. Alternatively, I could get the guarantee of Natural<T.Magnitude> from an UnsignedInteger & SystemsInteger constraint.

[oscbyspro]

Tangentially, it turns out that the discrete logarithm problem is trivial when the group size is a power of 2. But, everybody already knows that. No dice, but a fun rabbit hole nonetheless.