feat: Turtle.get_Duration default ( Fixes #270 )

Author: StartAutomating

Turtle.types.ps1xml

@@ -4065,9 +4065,14 @@ $this | Add-Member -MemberType NoteProperty -Force -Name '.Defines' -Value $newD
     Gets the duration
 .DESCRIPTION
     Gets the default duration of animations and morphs.
+
+    By default, 4.2 seconds.
 #>
-if ($this.'.Duration') { return $this.'.Duration'}
-return
+if ($null -eq $this.'.Duration') { 
+    $this | Add-Member NoteProperty '.Duration' ([timespan]::FromSeconds(4.2)) -Force
+}
+return $this.'.Duration'
+
                     </GetScriptBlock>
         <SetScriptBlock>
                         &lt;#