feat: add property path support

src/request.validation/Problem.cs

@@ -11,7 +11,7 @@ public record Problem
 	/// <summary>
 	/// The name of the property.
 	/// </summary>
-	public required string PropertyName { get; init; }
+	public required PropertyPath PropertyPath { get; init; }
 
 	/// <summary>
 	/// Custom severity level associated with the failure.