FakeMultipeerService.sentMessages is an unsynchronized array (latent TSan race)

[darioalessandro]

RemoteCamTests/SessionTestSupport.swift:25

var sentMessages: [(msg: Message, peers: [MCPeerID], mode: MCSessionSendDataMode)] = []
...
sentMessages.append((msg, peers, mode))   // :44 — from the coordinator's actor context

Appended from the coordinator's actor while tests read it from the test thread — the same data race that made LoopbackMultipeerService.sentMessages crash 5 of 10 runs under Thread Sanitizer (fixed in PR #157, commit 4d81746).

This one isn't what TSan currently trips on, so it was left alone deliberately — but it's the same latent shape and will bite as soon as a test reads it while the actor is still sending.

Fix (same shape as the one already landed)

private let sentMessagesStorage = Locked<[(msg: Message, peers: [MCPeerID], mode: MCSessionSendDataMode)]>([])
var sentMessages: [(msg: Message, peers: [MCPeerID], mode: MCSessionSendDataMode)] {
    get { sentMessagesStorage.value }
    set { sentMessagesStorage.value = newValue }
}

plus sentMessagesStorage.mutate { $0.append(...) } in send. Keeping the property's name and type means all existing reads and removeAll() calls compile untouched (~14 sites in RemoteCamSessionTests).

Locked<T> is in RemoteCam/Locked.swift, reachable from tests via @testable import RemoteShutter.