refactor: move CutParameters to OpenNest.Api namespace with new properties

Relocates CutParameters from OpenNest namespace to OpenNest.Api, adds
LeadInLength and PostProcessor properties, and provides a typed Default
factory. Updates Timing.cs, the WinForms project reference, and the three
consuming forms to resolve the type from the new namespace.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest.Core/Timing.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using OpenNest.Api;
 using OpenNest.CNC;
 using OpenNest.Converters;
 using OpenNest.Geometry;