feat: add produceBlockV4WithBid endpoint

[eth2353]

Motivation

Implement Beacon APIs #627, allowing validator clients to supply a selected execution payload bid. This avoids duplicate builder requests when producing blocks through multiple beacon nodes.

Description

• Add POST /eth/v4/validator/blocks/{slot}/with_bid with JSON and SSZ support.
• Reuse produceBlockV4 production logic and response codecs.
• Validate the supplied bid, apply the requested boost factor, and fall back to local production when the bid is invalid or the circuit breaker is active.
• Add coverage for request handling, bid selection, validation failures, and payload inclusion.

Validation:

• 139 targeted tests and lint pass.
• Type checking reports the same 13 errors as the unchanged baseline.
• Manually tested on a local Kurtosis devnet.

AI Assistance Disclosure

• External Contributors: I have read the contributor guidelines and disclosed my usage of AI below.

This PR’s implementation and tests were written primarily by OpenAI Codex (GPT-6 Astra High), with human review and direction.

[nflaig]

this test is kinda useless, this should be covered by spec tests already

[nflaig]

I don't like the diff in this file at all 😅