Implement BitOr and BitOrAssign for the NonZero integer types
This provides overloaded operators for `NonZero$Int | NonZero$Int`, `NonZero$Int | $Int`, and `$Int | NonZero$Int`. It also provides `BitOrAssign` where `self` is `NonZero$Int`, for symmetry.
It's a pretty small conceptual addition, but is good becasue but avoids a case where the operation is obviously sound, but you'd otherwise need unsafe to do it.
In crates trying to minimize `unsafe` usage, this is unfortunate and makes working with `NonZero` types often not worth it, even if the operations you're doing are clearly sound.
I've marked these as stable as I've been told in the past that trait impls are automatically stable. I'm happy to change it to unstable if this wasn't correct information.
I'm not entirely confident what version I should have put down, so I followed https://www.whatrustisit.com. Hopefully it's correct for this.
Apologies in advance if this has come up before, but I couldn't find it.
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