Add enhancements to progress widget

* Adds TransferSpeedColumn
* Adds DownloadedColumn
* Adds ElapsedTimeColumn
* Minor enhancements to existing columns

src/Spectre.Console/Extensions/Progress/SpinnerColumnExtensions.cs

@@ -23,5 +23,40 @@ namespace Spectre.Console
             column.Style = style;
             return column;
         }
+
+        /// <summary>
+        /// Sets the text that should be shown instead of the spinner
+        /// once a task completes.
+        /// </summary>
+        /// <param name="column">The column.</param>
+        /// <param name="text">The text.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static SpinnerColumn CompletedText(this SpinnerColumn column, string? text)
+        {
+            if (column is null)
+            {
+                throw new ArgumentNullException(nameof(column));
+            }
+
+            column.CompletedText = text;
+            return column;
+        }
+
+        /// <summary>
+        /// Sets the completed style of the spinner.
+        /// </summary>
+        /// <param name="column">The column.</param>
+        /// <param name="style">The style.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static SpinnerColumn CompletedStyle(this SpinnerColumn column, Style? style)
+        {
+            if (column is null)
+            {
+                throw new ArgumentNullException(nameof(column));
+            }
+
+            column.CompletedStyle = style;
+            return column;
+        }
     }
 }