Replace primitives_types with uint

[conradoplg]

Motivation

We need to use the recent zcash_primitives in librustzcash for ZIP-244/221 support. However, they have updated their dependencies to use bitvec 0.22, while we use 0.17. Due to a package conflict issue with funty, we must then update all dependencies that use bitvec.

One of those is primitive-types, however it hasn't been updated to use bitvec 0.22, and was due to being replaced in #829 anyway. That issue proposes replacing it with bigint, however that package has a different API and it will take some time to adapt to it.

Until we do that, we can use uint instead (which primitives-types also uses and therefore does not require any big changes in our code). This will unblock further work on the librustzcash update and we can eventually use bigint instead per #829.

Specifications

N/A

Designs

N/A

Solution

Use uint to define a U256 type which is essentially the same as the one defined in primitive-types.

Note that this does not prevent the packages conflicts by itself, we keep using bitvec 0.17 here. That will be solved in a separated PR because the bitvec upgrade is non-trivial and requires some code changes.

Review

Anyone can review, it's a simple change.

This blocks further work on the librustzcash update which is necessary to merge ZIP-244 PRs.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

In #829 we'll change it again to use bigint in order to have the same dependency as librustzcash.

[jvff]

Looks good to me :)

[dconnolly]

👍