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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

SawCut/Bin.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Runtime.Remoting.Messaging;
 
 namespace SawCut
 {
@@ -70,8 +69,8 @@ namespace SawCut
 
         public override string ToString()
         {
-            var totalLength = Helper.ConvertToMixedFraction(Math.Round(Length, 4));
-            var remainingLength = Helper.ConvertToMixedFraction(Math.Round(RemainingLength, 4));
+            var totalLength = FormatHelper.ConvertToMixedFraction(Math.Round(Length, 4));
+            var remainingLength = FormatHelper.ConvertToMixedFraction(Math.Round(RemainingLength, 4));
             var utilitation = Math.Round(Utilization * 100, 2);
 
             return $"Length: {totalLength}, {remainingLength} remaining, {Items.Count} items, {utilitation}% utilization";