fix: use UintBn64 for gloas ExecutionPayloadBid.executionPayment

[lodekeeper]

ExecutionPayloadBid.executionPayment is a uint64 with no bound in process_execution_payload_bid. Back it with UintBn64 (exact) instead of UintNum64 (float64, lossy above 2**53) so the bid hashTreeRoot stays exact across the full uint64 range. Gloas-only, no mainnet impact.

[nflaig]

this seems valid to me, that's why adding useless fields like execution_payment to the spec containers is bad, at least found this before any public testnet/mainnet, the reason why this is problematic is because we would produce a different HTR if such a bid was in a canonical block, causing a consensus split, not sure why we use number here, this field can be arbitrarily controlled by a proposer (or builder if bid is accepted)

[markolazic01]

looks good, I checked that changes properly cover all places where executionPayment appears.

[lodekeeper]

Thanks @markolazic01 for double-checking the executionPayment usages 🙏

@nflaig — agreed on all counts. The number (UintNum64) here was almost certainly a reflexive mirror of how we type the other uint64 payload fields — ExecutionPayload.gasLimit/gasUsed/blockNumber/timestamp are all UintNum64 too. That's fine for those: they're bounded well below 2^53 by validity rules every client enforces, so no client ever hashes an out-of-range value. The bid is the exception — executionPayment is proposer/builder-supplied on a signed container with no such bound, so its hash_tree_root is taken over whatever value they put in. UintNum64 silently truncates anything ≥ 2^53, so Lodestar would compute a different HTR than clients using exact uint64 → a canonical block carrying such a bid → block-root disagreement → consensus split. Same class as the Eth1Data.depositCount fix (#9747): proposer-controlled uint64 + no validity bound + float64 decode. UintBn64 keeps the exact bytes through SSZ/HTR. And agreed — much better to catch it pre-testnet/mainnet.

[nflaig]

must be done, this field can be controlled by the proposer or builder, gonna merge this