Use `NonZeroU64` in the new `InlineArray` so the compiler can optimize around it

I notice that the new `InlineArray` is based on a `[u8; 8]` that then gets converted to its different kinds. Its base representation should be a `NonZero`, since it appears that all valid bit patterns of it are intended to be nonzero. The compiler can then optimize things like `Option<NonZeroU64>` to be only `u64` sized and greatly improve the padding of structs that use it.