fix: restore XML documentation comment syntax

Change `// <summary>` back to `/// <summary>` for proper XML
documentation generation. Also removed outdated cache reference
from the comment since attributes are now passed directly.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: thomhurst

TUnit.Core/TestDetails.cs

@@ -65,9 +65,8 @@ public IEnumerable<T> GetAttributes<T>() where T : Attribute
             ? attrs.OfType<T>()
             : [];
 
-    // <summary>
+    /// <summary>
     /// Gets all attributes as a flattened collection.
-    /// Cached after first access for performance.
     /// </summary>
     /// <returns>All attributes associated with this test.</returns>
     public IReadOnlyList<Attribute> GetAllAttributes() => _allAttributes;