Rename SawCut library to CutList.Core

Rename the core library project from SawCut to CutList.Core for consistent
branding across the solution. This includes:
- Rename project folder and .csproj file
- Update namespace from SawCut to CutList.Core
- Update all using statements and project references

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CutList.Core/Tolerance.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace CutList.Core
+{
+    public static class Tolerance
+    {
+        public const double Epsilon = 0.00001;
+
+        public static bool IsEqualTo(this double a, double b, double tolerance = Epsilon)
+        {
+            return Math.Abs(b - a) <= tolerance;
+        }
+    }
+}