Add ItemConfiguration as property to ItemMetadata

The majority of the `ItemConfiguration` properties represent attributes (and their values) associated with individual parameters, properties, or methods, and whose values will not change at runtime. Given that, reidentifying these for every property incurs some overhead, and especially when we already have an `ItemMetadata` class for caching this information (via `TypeAccessor` and `TypeAccessorCache`).

The one exception to this is the `attributePrefix` constructor argument, which conditionally updates the `AttributeKey` property. That is passed to calls to e.g. the `TopicMappingService` and `ReverseTopicMappingService`. In subsequent updates, that will be removed from the `ItemConfiguration`, and managed internally within those classes.

Author: JeremyCaney

OnTopic/Internal/Reflection/ItemMetadata.cs

@@ -6,6 +6,9 @@
 using System.Collections;
 using System.Reflection;
 using OnTopic.Attributes;
+using OnTopic.Mapping;
+using OnTopic.Mapping.Internal;
+using OnTopic.Mapping.Reverse;
 
 namespace OnTopic.Internal.Reflection {
 
@@ -24,6 +27,7 @@ internal abstract class ItemMetadata {
     private readonly            ICustomAttributeProvider        _attributeProvider;
     private readonly            Type                            _type                           = default!;
     private                     List<Attribute>                 _customAttributes               = default!;
+    private                     ItemConfiguration?              _itemConfiguration;
 
     /*==========================================================================================================================
     | CONSTRUCTOR
@@ -102,6 +106,26 @@ bool isList()
       }
     }
 
+    /*==========================================================================================================================
+    | CONFIGURATION
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Gets a reference to the configuration settings for the current item, based on the annotations configured in the code.
+    /// </summary>
+    /// <remarks>
+    ///   The <see cref="ItemConfiguration"/> class identifies annotations used by the <see cref="TopicMappingService"/> and the
+    ///   <see cref="ReverseTopicMappingService"/>. While it can be called on any <see cref="Type"/>, it is only expected to
+    ///   offer a benefit for model classes intended for mapping.
+    /// </remarks>
+    internal ItemConfiguration Configuration {
+      get {
+        if (_itemConfiguration is null) {
+          _itemConfiguration = new(this, Name, "");
+        }
+        return _itemConfiguration;
+      }
+    }
+
     /*==========================================================================================================================
     | IS NULLABLE?
     \-------------------------------------------------------------------------------------------------------------------------*/