This simple refactoring PR changes the interface for the SipHash arbitrary-data Write method to take a Span<unsigned char> instead of having to pass data and length. (Span<std::byte> seems to be more modern, but vectors of unsigned char are still used prety much everywhere where SipHash is called, and I didn't find it very appealing having to clutter the code with Make(Writable)ByteSpan helpers).

ninja all check-all