Make Error use NonZero for its value

[Darksonn]

Currently, the type Result<(), Error> takes up twice the size that it needs to. By changing the type inside Error to be the appropriate NonZero* type will make the niche optimization apply to reduce the size.

Related to #195.

[felipeagger]

I will work on it.

[ojeda]

https://lore.kernel.org/rust-for-linux/CANiq72kMg=HKkuTTUhGDmCamgJ1c1JSM8HZyUKwA9yi_6nF3iQ@mail.gmail.com/