Specify how to handle conflicting bids

[ralexstokes]

This is a bit of an edge case but I think it is worth specifying that if a proposer (with the boost software acting as a proxy) receives multiple signed builder bids with the same value but differing payload headers, the proposer should break the tie with the hash tree root of the signed bid (e.g. choose the lessor root interpreting the root as a 256-bit number)

[metachris]

Interesting idea! This would be an mev-boost internal implementation detail, since mev-boost will always provide only a single SignedBuilderBid to the proposer.