Add deneb signature checking for block contents

[avalonche]

📝 Summary

Adds signature verification to the blobs and tests. Don't have tests for Deneb signatures as it wasn't easy to get test data from devnets (signed block v2 endpoint only returned the signed beacon block but not signed blob sidecars)

⛱ Motivation and Context

📚 References

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✅ I have run these commands

• make lint
• make test-race
• go mod tidy
• I have seen and agree to CONTRIBUTING.md

[codecov-commenter]

Codecov Report

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Flag	Coverage Δ
unittests	33.43% <0.00%> (?)

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