This conditional implies that get_latest_attesting_balance applies the proposer score boost only to the proposer's block, but not its ancestors. This is not the correct method to apply the proposer score boost.

The boost should be applied like usual LMD votes (i.e., store.latest_messages) - all ancestors of store.proposer_boost_root should get the additional weight.

generally should avoid multi-line ifs. This is also a bit secretly too pythonic (it assumes that if the first bool fails, the second is not executed, avoiding the undefined behavior if Root() being passed into get_ancestor

suggest somthing like the following

    if store.proposer_boost_root != Root():
        if get_ancestor():
            ...

An alternative, I personally prefer this:

    if store.proposer_boost_root == Root():
        return attestation_score
    proposer_score = Gwei(0)
    if get_ancestor():
        ...
    return attestation_score + proposer_score

I think that very nicely reads as "If proposer_boost is not enabled, just return the attestation_score, otherwise calculate the proposer score and return the sum"