[WIP / R&D] - EELS backend with eth-tester

[fselmo]

Implement a rough but "working" EELSBackend for EthereumTester (eth-tester) for research into a new and very relevant backend to test JSON-RPC calls against.

• I made some changes on my personal fork of the execution-specs repo to fix dependency resolution issues for now, but the way the consensus-specs dynamically installs ruamel.yaml and marko does not make it a very straightforward dependency to work with. I replaced the kzg implementations with ckzg and there was a lot less friction.
• For now this PR uses commits on my forks of both eth-tester and execution-specs repositories.
• This is currently a significantly slower EVM as our test suite will show but I believe at least part of that is due to my rough implementation and some validation approaches I took to get this "working".
• Added pypy eels and py-evm backend runs as well.

Todo:

• Get all tests passing
• Clean up commit history
• Add or update documentation related to these changes
• Add entry to the release notes

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