style(io): apply consistent formatting and remove unused usings

Whitespace/indentation cleanup (formatter pass) plus unused using
directives. No behavior change.

OpenNest.IO/Bending/SolidWorksBendDetector.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;

OpenNest.IO/ChrFont.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;

OpenNest.IO/Extensions.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Drawing;
-using System.Linq;
 using ACadSharp.Entities;
 using CSMath;
 using OpenNest.Geometry;

OpenNest.IO/NestWriter.cs

@@ -5,7 +5,6 @@ using System.IO.Compression;
 using System.Linq;
 using System.Text;
 using System.Text.Json;
-using OpenNest.Bending;
 using OpenNest.CNC;
 using OpenNest.Engine.BestFit;
 using static OpenNest.IO.NestFormat;

OpenNest.IO/ProgramReader.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;

OpenNest.IO/SplitDxfWriter.cs

@@ -7,7 +7,6 @@ using ACadSharp.Tables;
 using CSMath;
 using OpenNest.Bending;
 using OpenNest.Converters;
-using OpenNest.Geometry;
 // Disambiguate Entity — both ACadSharp.Entities and OpenNest.Geometry define it
 using GeoEntity = OpenNest.Geometry.Entity;