re-factor(weld): move current tests to json_infra

[gurukamath]

(closes #1352)

What was wrong?

Currently, every fork has its own tests folder. So does the EEST repository. In a post-weld world, this could get really messy. Hence, execution-specs need to have a simpler test folder structure to enable the EEST test folders to seamlessly move into the repository.

Related to Issue #1352

How was it fixed?

This PR performs the following changes

1. Re-factors and moves all the fork specific tests (primarily the blockchain tests and the state tests) in the json_infra folder
2. Make the test running less verbose and more maintainable.
3. Removes the difficulty tests which were not running until now anyway in the CI
4. Removes the fork specific rlp tests. There is enough rlp encoding and decoding happening in the json fixture tests that these tests are largely redundant.

Cute Animal Picture

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.26%. Comparing base (87a9e65) to head (90de63b).
⚠️ Report is 1 commits behind head on forks/osaka.

Additional details and impacted files

@@               Coverage Diff               @@
##           forks/osaka    #1360      +/-   ##
===============================================
+ Coverage        94.15%   94.26%   +0.10%     
===============================================
  Files              583      583              
  Lines            34666    34666              
  Branches          3070     3070              
===============================================
+ Hits             32641    32677      +36     
+ Misses            1492     1454      -38     
- Partials           533      535       +2     

Flag	Coverage Δ
unittests	94.26% <ø> (+0.10%)	⬆️

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[SamWilsn]

Removes the fork specific rlp tests. There is enough rlp encoding and decoding happening in the json fixture tests that these tests are largely redundant.

Is there anything we should move into ethereum-rlp?

[gurukamath]

Is there anything we should move into ethereum-rlp?

Actually most of these tests use fork related types like Header, Transaction etc. And I don't think these contribute significantly to testing the spec. So, I'd still be in favor of just getting rid of them

[gurukamath]

@SamWilsn Have updated the PR based on the feedback