[Feature] Make prague field and enum

[mattsse]

Component

rpc

Describe the feature you would like

starting with prague the CL sends a list of requests alongside the actual payload:

alloy/crates/rpc-types-engine/src/sidecar.rs

Lines 16 to 18 in b621af0

	/// The EIP-7685 requests provided as additional request params to `engine_newPayloadV4` that
	/// are not present in the `ExecutionPayload`.
	prague: Option<Requests>,

the requests are never stored be the EL because not part of the block.
to mimick consensus, mostly for testing this makes it difficult and we want a way to provide just the requests hash instead

TODO

• introduce an enum that has either a list of requests or an hash
• expose a requests_hash function on that enum

Additional context

No response

[0xriazaka]

Can i take this?