feat(json): introduce MarshalJSONHex

[itsdevbear]

A bit of an edge case, but cannot seem to get payload unmarshalling to be happy.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 99.88%. Comparing base (ce90883) to head (8e56e89).

Additional details and impacted files

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##            master     #182      +/-   ##
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- Coverage   100.00%   99.88%   -0.12%     
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  Files            5        5              
  Lines         1666     1668       +2     
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  Hits          1666     1666              
- Misses           0        2       +2     

[holiman]

I don't quite see the point of this. The MarshalJSONHex is not part of any interface that I know of, so it cannot be auto-detected and used by encoders. And if you need to explicitly use it, you might aswell just use Hex() directly.

[itsdevbear]

I was torn about this PR as well. The reason here was to provide api surface to allow uint256's to be used in an ExecutionPayload more naturally.

In geth right now you have to write a custom marshal function if the consensus side type of your ExecutionPayload uses a uint256, else geth will freak out.

This is the broader issue i'm trying to tackle, open to other suggestions

[holiman]

In geth right now you have to write a custom marshal function if the consensus side type of your ExecutionPayload uses a uint256, else geth will freak out.

How does this PR make any difference, though?