Exclude empty outputs in requests

[rjnrohit]

Changes

Implements changes from these spec PRs:

• Update EIP-7685: exclude empty requests data in commitment ethereum/EIPs#8989
• engine: exclude empty requests in requests list ethereum/execution-apis#599

Types of changes

1. Exclude the empty requests from hash calculation
2. Add type prefix byte to the ExecutionRequests for the engineAPIs

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

Testing

Requires testing

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• No

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Documentation

Requires documentation update

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[MarekM25]

Let's hold off on merging this for now as it may break Mekong. The changes look good overall.