deps: update uint256 to 1.2.0

[holiman]

1.2.0 mainly contains some conversions, and also API-changes to make it more closely resemble a big.Int, and fixes an error in SubUint64 (which is unused in our code) .

[royalfork]

@holiman Thanks for your lovely uint256 package, but your latest release violates the rules of semantic versioning. It introduces a breaking API change; the function signature changes from uint256.NewInt() to uint256.NewInt(uint64). Because go mod assumes that go-ethereum should be able to use uint256 v1.X without any additional code changes, any project which depends on both uint256 (v1.2.0) and go-ethereum will break.

Before merging this, maybe you'd like to consider renaming the uint256 v1.2.0 release to v2.0.0? This will have the added benefit of unbreaking other projects which depend on uint256.

[holiman]

Yes, that's true. I considered it, but the thing with major version updates is that it requires you to keep the original code intact, and copy the whole codebase to a v2 folder.

I felt that it was a bit overkill. Yes, the API changed, but not in a 'dangerous' way (for example, like a database which changes the db on-disk format in a backwards-incompatible way), only in a small way which should be easy to fix. I didn't think that a lot of projects were using uint256 -- it's mainly written with go-ethereum in mind.

I went through the major-upgrade excercise when I upgraded the holiman/bloomfilter to a v2, and it was a pretty sizeable amount of work in the end.

Apologies for any problems caused!