Fix named parameters normalization issue

Co-authored-by: Constantine Nathanson <constantine@cloudinary.com>

Author: YomesInc

CloudinaryDotNet.Tests/Transformations/Common/ExpressionTest.cs

@@ -322,6 +322,8 @@ public void TestShouldSupportPowOperator()
         [TestCase("foo&&bar", "foo&&bar")]
         [TestCase("width", "w")]
         [TestCase("initial_aspect_ratio", "iar")]
+        [TestCase("duration", "du")]
+        [TestCase("preview:duration", "preview:duration")]
         [TestCase("$width", "$width")]
         [TestCase("$initial_aspect_ratio", "$initial_ar")]
         [TestCase("$mywidth", "$mywidth")]

CloudinaryDotNet/Transforms/BaseExpression.cs

@@ -69,6 +69,7 @@ public abstract class BaseExpression<T> : BaseExpression
             { "tags", "tags" },
             { "pageX", "px" },
             { "pageY", "py" },
+            { "duration", "du" },
         };
 
         /// <summary>
@@ -498,7 +499,7 @@ private static string GetPattern()
             }
 
             sb.Remove(sb.Length - 1, 1);
-            sb.Append(")(?=[ _])|(?<!\\$)(").Append(string.Join("|", parameters.Keys.ToArray())).Append("))");
+            sb.Append(")(?=[ _])|(?<![\\$:])(").Append(string.Join("|", parameters.Keys.ToArray())).Append("))");
             return sb.ToString();
         }
     }