Computes a width-(w) "Non-Adjacent Form" of this scalar.
Thanks to curve25519-dalek for the original implementation that informed this one.
The full scalar field MUST fit in 256 bits in this implementation.
The window width (must be >= 2 and <= 8)
The NAF representation as an array of signed bytes
A trait for transforming a scalar generic over a ciphersuite to a non-adjacent form (NAF).