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The three different request fields have been replaced by a single field.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 ethereum/execution-apis#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

[onbjerg]

After some thinking we likely do not gain much by retaining the type here instead of using blobs, since validation is mostly a CL responsibility now, and system contracts adhering to EIP-7685 return the requests pre-serialized. For user-facing RPC it will matter more, but at that point in time it's ok to pay for the ser/de cost, while we'd likely want to avoid it during execution.

Restructuring the PR.