chore: flatten eip-7685 requests into a single list

[onbjerg]

Motivation

The three different request fields have been replaced by a single field.

Requests over engine API will now be in an opaquely encoded format as defined by EIP-7685, and they will be in a single list.

See https://github.com/ethereum/execution-apis/pull/577

Solution

Theoretically this allows us to not encode or decode requests on the EL, since system contracts are expected to output requests in a pre-serialized format, ready to be pushed over engine API. We can also compute the requests hash and compare it to the one in the payload (if it is an external block) without encoding or decoding.

However, we decided to retain type safety, so we do not gain from this, and we will still be encoding and decoding in the hot path. This also means we now depend on alloy-consensus in alloy-rpc-types-beacon.

Draft Status

This currently lacks

• doc updates
• serializing requests with Eip7685Encodable when serializing the requests as JSON for engine API

PR Checklist

• [ ] Added Tests
• [ ] Added Documentation
• [ ] Breaking changes