U256 type can get negative value

[RostislavLitovkin]

var address = "unixuHLc4UoAjwLpkQHUWy2NpT5LV4tUqJFnFVNyLaeqBfq22";

var publicKey = Utils.GetPublicKeyFrom(address);

var value = new U256();

int p = 0;

value.Decode(publicKey.Reverse().ToArray(), ref p);

Console.WriteLine(value.Value); // -26843990603843339315797176730311565364345939525783601353920003531657203886725

U256 should never be negative.

[RostislavLitovkin]

Workaround I found for getting the correct value:

Console.WriteLine(new BigInteger(publicKey, true, true));

[darkfriend77]

NetStandard 2.0 doesn't support the isUnsigned option. The trade-off is to mimic a larger array to achieve a BigInteger with the most significant bit not set. However, this leads to an inconsistency between the BigInteger value and the byte representation.

I'm unsure if we should address this, as the use case seems quite constructed and likely irrelevant.

https://github.com/SubstrateGaming/Substrate.NET.API/commit/a47945da924b4b6bda88b8b098a4d8e6a7cab565#diff-d9432c6f40e795d58bd62982772a902b84fac034ad1ef8c55ac543a4d4f8086eR80