Add flat encoding and requests as a side car

[rjnrohit]

Closes #7525
Closes #7524
Closes #7522
Resolves #7521

Changes

Implements changes from

• Update EIP-6110: change request to flat encoding EIPs#8856
• Update EIP-7685: change requests hash to flat hash EIPs#8854
• engine: unified list of opaque requests  execution-apis#577
• engine: Make execution requests a sidecar, take 2 execution-apis#591

Types of changes

• PR modifies two existing engine APIs : engine_getPayloadV4 and engine_getPayloadV4, It incorporates suggestions from pectra-devnet4 doc, which was to exchange requests as a side car and remove them from the block body
• It removes two engine APIs: engine_getPayloadBodiesByRangeV2 and engine_getPayloadBodiesByHashV2 and all related objects and handlers, which are now obsolete.
• It introduces a new processor called IExecutionRequestsProcess and gets rid of all kinds of exiting requests processors.
• Add support for flat request encoding and therefore, a new way for RequestsHash calculation, more info at: https://eips.ethereum.org/EIPS/eip-7685

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

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

Notes on testing

Few more tests are yet to be written after a few rounds of discussions.

Documentation

Requires documentation update

• Yes
• No

Remarks

Please verify the requestsHash calculation, which should be done as follow:

def compute_requests_hash(requests):
    m = sha256()
    for r in requests:
        m.update(sha256(r))
    return m.digest()

block.header.requests_hash = compute_requests_hash(requests)

[MarekM25]

a few comments and here the most important:
have you tried to run devnet-4 fixtures from EF testing team?

[LukaszRozmej]

Part review for now

[LukaszRozmej]

why merged?

[rjnrohit]

why merged?

It was merged because there was confusion between me and @ak88, we were discussing that there should be one branch for devnet-4 changes, i.e., pectra-devnet-4. So @ak88 merged it!