NonZero* types for BigInt and related numbers

[ActuallyHappening]

Hey guys,

I'm wanting to express certain invariants in my rust types while also handling arbitrarily large numbers, and so was refactoring from NonZeroI32 to NonZeroBigInt when I realised that NonZeroBigInt doesn't actually exist, and no analogue to this type already exists.

Even if the compiler doesn't do niche-value optimisation as I think NonZeroI32 and related std library types do, can we still get a type NonZeroBigInt and related types (e.g. NonZeroBigUInt)?
Thanks

[cuviper]

It's possible to express this, but I am adverse to duplicating a bunch of API surface on such types, and there would not be any niche benefit since the value is behind a heap allocation. We do already get niches from the inner Vec though, which was greatly expanded in rust-lang/rust#106790 too.