Implement pectra-devnet-4 changes

[yperbasis]

https://notes.ethereum.org/@ethpandaops/pectra-devnet-4

• [x] EIP-7251 address update: Done - https://github.com/ethereum/EIPs/pull/8889
• [ ] Block body requests header update: Awaiting merge - https://github.com/ethereum/EIPs/pull/8908
• [ ] Change to Engine API for requests (flattening): Awaiting merge - https://github.com/ethereum/execution-apis/pull/591
• [ ] Change deposits to flat encoding: Awaiting merge - https://github.com/ethereum/EIPs/pull/8856
• [ ] Change withdrawal reqs to flat encoding: Todo - https://github.com/ethereum/EIPs/pull/8855
• [ ] Change reqs hash to flat hash: Todo - https://github.com/ethereum/EIPs/pull/8854
• [ ] Change consolidation reqs to flat encoding: Todo - https://github.com/ethereum/EIPs/pull/8854

Also, awaiting release of pectra-devnet-4 tests release at https://github.com/ethereum/execution-spec-tests/pull/832

[somnathb1]

Priority high here means importance, not all EIPs in the list have been merged/finalized yet for pectra-devnet-4. The issue is expected to remain open for some time till the EIPs are finalized. The code changes will be accumulated over multiple PRs referencing this issue.