Echo bidder identity and qualify pre-auction rejections on the auction response

[dsabonis]

The signed attestation deliberately carries no bidder identity: AuctionAttestationUserData is shared with SDKs and bidders, so the winner and runner-up are attested as CoreBidWithoutBidder (bid ID, price, currency, deal ID, media type only). The host then has to reconstruct which bidder each attested bid belongs to — and bid IDs are only unique per bidder, so when IDs collide across bidders in a round the reconstruction is ambiguous.

This adds WinnerBidder and RunnerUpBidder to EnclaveAuctionResponse, populated from the auction result. They echo the Bidder field the host itself supplied on the request bids, so they reveal nothing to the host that it does not already know, and they are plain envelope fields — not part of the signed COSE user data, which stays bidder-free. Only the winner and runner-up identities are echoed, never the full bid list.

Both fields are omitempty and additive: hosts that don't read them see an unchanged response, and hosts that do read them treat them as an unsigned hint (the attested bid ID, price, and media type remain the authoritative record).

Testing

• go test ./... — the ProcessAuction ranking tests now also assert the echoed identities (including under adjustment factors, where the echo must follow the adjusted ranking).

[nickpell]

I added a commit to make the rejection lists bidder-qualified, to enable correct assignment of the loss reason. Feel free to modify that commit.

Looks ready to merge - 👍 on keeping the bidder names out of the attestation, that's a great way to maintain the current contract along with better management of the bids.