fakeDealSessionGroup
fun fakeDealSessionGroup(playerIds: List<PeerId>, newScheme: () -> CommutativeScheme = { SraScheme() }, scope: CoroutineScope): List<DealSession>
Build a wired group of DealSessions (one per id in playerIds, in order) over a fakeSeamGroup, each running its own instance from newScheme and holding a key that instance minted — the N-player generalisation of fakeDealSessionPair, and per-player separate for the same reason.