Add foundation

Toolkit.Foundation/AsyncLock.cs

@@ -0,0 +1,23 @@
+using System.Runtime.CompilerServices;
+
+namespace Toolkit.Foundation;
+
+public class AsyncLock(int initial = 1, 
+    int maximum = 1) : 
+    IDisposable
+{
+    private readonly SemaphoreSlim semaphore = new(initial, maximum);
+
+    public void Dispose()
+    {
+        semaphore.Release();
+    }
+
+    public TaskAwaiter<AsyncLock> GetAwaiter() => LockAsync().GetAwaiter();
+
+    private async Task<AsyncLock> LockAsync()
+    {
+        await semaphore.WaitAsync();
+        return this;
+    }
+}