Device deactivation (#4963)

* Device deactivation

* Check active status in service

* Format and work around potential deadlocks

src/Core/Entities/Device.cs

@@ -38,6 +38,10 @@ public class Device : ITableObject<Guid>
     /// </summary>
     public string? EncryptedPrivateKey { get; set; }
 
+    /// <summary>
+    /// Whether the device is active for the user.
+    /// </summary>
+    public bool Active { get; set; } = true;
 
     public void SetNewId()
     {