Allow multiple async polling expectations (#1189)

This partially solves the issue of swift testing's concurrent test runner tripping the 'nested polling expectation' error.
Solving this for synchronous polling expectations will be much more involved.
As synchronous polling expectations actually run all the test code on the main runloop.

Author: younata

Sources/Nimble/Utils/AsyncAwait.swift

@@ -60,7 +60,7 @@ internal enum AsyncPollResult<T> {
 internal actor AsyncPromise<T> {
     private let storage = Storage()
 
-    private final class Storage {
+    private final class Storage: @unchecked Sendable {
         private var continuations: [UnsafeContinuation<T, Never>] = []
         private var value: T?
         // Yes, this is not the fastest lock, but it's platform independent,
@@ -142,7 +142,8 @@ private func timeout<T>(timeoutQueue: DispatchQueue, timeoutInterval: NimbleTime
     let semTimedOutOrBlocked = DispatchSemaphore(value: 0)
     semTimedOutOrBlocked.signal()
 
-    DispatchQueue.main.async {
+    let timeoutQueue = DispatchQueue(label: "org.quick.nimble.timeoutQueue", qos: .userInteractive)
+    timeoutQueue.async {
         if semTimedOutOrBlocked.wait(timeout: .now()) == .success {
             timedOutSem.signal()
             semTimedOutOrBlocked.signal()
@@ -202,14 +203,6 @@ private func runPoller(
     sourceLocation: SourceLocation,
     expression: @escaping () async throws -> PollStatus
 ) async -> AsyncPollResult<Bool> {
-    awaiter.waitLock.acquireWaitingLock(
-        fnName,
-        sourceLocation: sourceLocation
-    )
-
-    defer {
-        awaiter.waitLock.releaseWaitingLock()
-    }
     let timeoutQueue = awaiter.timeoutQueue
     return await withTaskGroup(of: AsyncPollResult<Bool>.self) { taskGroup in
         taskGroup.addTask {