Add serde support

[widberg]

Basic Serialize and Deserialize implementations for UInt<T, BITS> with graceful error handling and tests, gated by serde feature. A step towards closing hecatia-elegua/bilge#74.

[hecatia-elegua]

looks solid, but does serde not have some kind of error so we would not need InvalidUIntValueError?
(I have not looked into it)

[danlehmann]

Apologies for the slow response! (I originally got this patch while I was on vacation and lost track of it when I returned).

But apologies aside, I've been trying to find a reviewer this morning (as I don't really know serde) - I'd like to merge this asap. If no one is willing to do it, I'll have to read up a bit on serde

[widberg]

looks solid, but does serde not have some kind of error so we would not need InvalidUIntValueError? (I have not looked into it)

If you can find a way to make Serde's Unexpected take a 128-bit int I'd be happy to do that, but as far as I can see it only takes a 64-bit int. This is because 128-bit support in Serde came later and changing the API now would require a bump in the major version number. The InvalidUIntValueError was my solution to this but I'm open to ideas :)

[hecatia-elegua]

@widberg oh sorry, you have commented that in code. I think it's a good solution :)

[danlehmann]

Thanks for your contribution and sorry for being so slow!

[danlehmann]

I'll enable the github tests in a follow-up