Implements some micro-optimizations

PkmnLib.Static/Item.cs

@@ -132,7 +132,7 @@ public interface IItem : INamedValue
     /// </summary>
     /// <param name="key">The flag to check for.</param>
     /// <returns>True if the item has the flag, false otherwise.</returns>
-    bool HasFlag(string key);
+    bool HasFlag(StringKey key);
 }
 
 /// <inheritdoc />
@@ -206,5 +206,5 @@ public class ItemImpl : IItem
     }
 
     /// <inheritdoc />
-    public bool HasFlag(string key) => Flags.Contains(key);
+    public bool HasFlag(StringKey key) => Flags.Contains(key);
 }