Refactor Helper to FormatHelper with improved documentation

- Rename Helper class to FormatHelper for clarity
- Add comprehensive XML documentation
- Update all references in BinFileSaver, ArchUnits, and Bin
- Remove unused System.Drawing import
- Better method documentation explaining parameters and return values

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

SawCut/ArchUnits.cs

@@ -60,7 +60,7 @@ namespace SawCut
         public static string FormatFromInches(double totalInches)
         {
             var feet = Math.Floor(totalInches / 12.0);
-            var inches = Helper.ConvertToMixedFraction(totalInches - (feet * 12.0));
+            var inches = FormatHelper.ConvertToMixedFraction(totalInches - (feet * 12.0));
 
             if (feet > 0)
             {