Several refactorings to testing

[leolara]

In this PR:

• I port one of the 7 formats introduced yesterday to the framework we are using reducing potentially the number of repeated code (considering the boilerplate in kzg_4844_legacy.py that is implemented elsewhere).
• Enable these tests to run in pytest so allow to future use of the pytest plugins from STEEL.
• Dramatically reduce the start time of generated tests, but refactoring a test that was being executed always at collection phase.

Note: this PR is based on the new caching system PR, to keep the non-multithread caching that was already implemented in kzg_4844_legacy in the refactored version. #4440

[jtraglia]

Hey Leo, yeah the proof of concept looks fine. Templates look nice. Just some random feedback:

• These will be run with make test which isn't really what we wanted, but that's fine.
  • I expect they will make CI checks considerably slower.
• These are now under the kzg_4844 runner when they should be in kzg.
  • See https://github.com/ethereum/consensus-spec-tests/tree/master/tests/general/deneb/kzg
• These are no longer in the general directory like before:
  • They are now in both the minimal & mainnet, which also means they're executed twice.
  • Eg consensus-spec-tests/tests/{minimal,mainnet}/deneb/kzg_4844/blob_to_kzg_commitment/
  • Try running make reftests k=blob_to_kzg_commitment_case_valid_blob

PS: I merged a fix to the legacy tests which prevented other tests from working. See:

• Do not run KZG compute challenge tests in the collection phase #4546