feat(Factory): prevent service modifications after provider is built

Added an `IsBuilt` property and `EnsureNotBuilt()` helper to `Factory` class
to restrict modifications to the service collection once the service provider
has been built. This ensures immutability and prevents runtime inconsistencies
after initialization.

DigitalData.Core.Abstractions/Factory.cs

@@ -12,9 +12,10 @@ namespace DigitalData.Core.Abstractions
         public static readonly Factory Instance = new Factory();
 
         private readonly IServiceCollection _serviceCollection = new ServiceCollection();
-
         private readonly Lazy<IServiceProvider> _lazyServiceProvider;
 
+        private bool IsBuilt => _lazyServiceProvider.IsValueCreated;
+
         public Factory()
         {
             _serviceCollection = new ServiceCollection();
@@ -40,7 +41,11 @@ namespace DigitalData.Core.Abstractions
         public ServiceDescriptor this[int index]
         {
             get => _serviceCollection[index];
-            set => _serviceCollection[index] = value;
+            set
+            {
+                EnsureNotBuilt();
+                _serviceCollection[index] = value;
+            }
         }
 
         public int IndexOf(ServiceDescriptor item)
@@ -50,21 +55,25 @@ namespace DigitalData.Core.Abstractions
 
         public void Insert(int index, ServiceDescriptor item)
         {
+            EnsureNotBuilt();
             _serviceCollection.Insert(index, item);
         }
 
         public void RemoveAt(int index)
         {
+            EnsureNotBuilt();
             _serviceCollection.RemoveAt(index);
         }
 
         public void Add(ServiceDescriptor item)
         {
+            EnsureNotBuilt();
             _serviceCollection.Add(item);
         }
 
         public void Clear()
         {
+            EnsureNotBuilt();
             _serviceCollection.Clear();
         }
 
@@ -80,6 +89,7 @@ namespace DigitalData.Core.Abstractions
 
         public bool Remove(ServiceDescriptor item)
         {
+            EnsureNotBuilt();
             return _serviceCollection.Remove(item);
         }
 
@@ -93,5 +103,13 @@ namespace DigitalData.Core.Abstractions
             return (_serviceCollection as IEnumerable).GetEnumerator();
         }
         #endregion
+
+        #region Helpers
+        private void EnsureNotBuilt()
+        {
+            if (IsBuilt)
+                throw new InvalidOperationException("Service provider has already been built. No further service modifications are allowed.");
+        }
+        #endregion
     }
 }