Introduce `NewPayloadRequestHeader` for BIB

# Overview
With the introduction of block in blobs ([BIB](https://ethresear.ch/t/blocks-are-dead-long-live-blobs/24611)), validators are no longer required to download full blocks to verify payload availability. Instead, they can sample blobs via the standard DAS mechanism. As such, we introduce a new `NewPayloadRequestHeader` type, which contains the minimum data required to verify a block using execution proofs. This was initially introduced in EIP8025 but has since been removed as it is unnecessary in the absence of BIB.

https://github.com/ethereum/consensus-specs/blob/29d39d28fe7c20b49696cc2f541ae187a68f97bc/specs/_features/eip8025/beacon-chain.md?plain=1#L110-L119

Start by reading specs/_features/eip8025/beacon-chain.md at lines 110-119 and the surrounding BIB context. Identify where the NewPayloadRequestHeader type belongs and what minimum data is required for execution-proof verification. Done means the specification clearly defines the type and its verification role for BIB.

Written by the indexing model from the issue text.