feat(io): workbook part-quantity reader and cut-only import coverage

PartQuantityReader parses a Parts worksheet (Part Name / Qty Required)
with exact-name matching and strict rejection of invalid, fractional,
negative, or duplicate quantities. Cut-only import drops case-insensitive
ETCH/SCRIBE mark layers before geometry so bend detection cannot
regenerate them. Tests cover both.

OpenNest.IO.Tests/CutOnlyImportTests.cs

@@ -0,0 +1,68 @@
+using ACadSharp;
+using ACadSharp.IO;
+using CSMath;
+using OpenNest.CNC;
+using CadLayer = ACadSharp.Tables.Layer;
+using CadLine = ACadSharp.Entities.Line;
+
+namespace OpenNest.IO.Tests;
+
+public class CutOnlyImportTests
+{
+    [Theory]
+    [InlineData("ETCH")]
+    [InlineData("Scribe")]
+    [InlineData("sCrIbE")]
+    public void CutOnlyImportDropsMarksBeforeGeometryAndDoesNotRegenerateBends(string layer)
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"opennest-cut-only-{Guid.NewGuid()}.dxf");
+        try
+        {
+            var doc = new CadDocument();
+            var points = new[]
+            {
+                new XYZ(0, 0, 0),
+                new XYZ(10, 0, 0),
+                new XYZ(10, 10, 0),
+                new XYZ(0, 10, 0),
+            };
+            for (var i = 0; i < points.Length; i++)
+                doc.Entities.Add(new CadLine(points[i], points[(i + 1) % points.Length]));
+            // Marks outside the perimeter must not affect nesting bounds or become cut paths.
+            doc.Entities.Add(
+                new CadLine(new XYZ(-5, 5, 0), new XYZ(15, 5, 0)) { Layer = new CadLayer(layer) }
+            );
+            doc.Entities.Add(
+                new CadLine(new XYZ(0, 5, 0), new XYZ(10, 5, 0))
+                {
+                    Layer = new CadLayer("BEND"),
+                    LineType = new ACadSharp.Tables.LineType("CENTER"),
+                }
+            );
+            DxfWriter.Write(path, doc, false);
+            var drawing = CadImporter.ImportDrawing(
+                path,
+                new CadImportOptions { DetectBends = false, Quantity = 3 }
+            );
+            Assert.Empty(drawing.Bends);
+            Assert.Equal(4, drawing.SourceEntities.Count);
+            Assert.Equal(3, drawing.Quantity.Required);
+            Assert.Equal(100, drawing.Area, 6);
+            Assert.DoesNotContain(
+                drawing.Program.Codes.OfType<LinearMove>(),
+                m => m.Layer == LayerType.Scribe
+            );
+            var job = new NestJob(
+                new[] { DrawingJobMapper.FromDrawing("part", drawing, 3) },
+                new[] { new NestPlateStock("sheet", new OpenNest.Geometry.Size(30, 30), 1, 0.3) }
+            );
+            var result = new FixedStrategyNestingEngine("Strip").Solve(job);
+            Assert.Equal(NestJobStatus.Complete, result.Status);
+            Assert.Equal(3, Assert.Single(result.Fulfillment).Placed);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+}

OpenNest.IO.Tests/PartQuantityReaderTests.cs

@@ -0,0 +1,89 @@
+using ClosedXML.Excel;
+using OpenNest.IO.Bom;
+
+namespace OpenNest.IO.Tests;
+
+public class PartQuantityReaderTests
+{
+    [Fact]
+    public void ReadsExactNamesAndQuantitiesIncludingZeroDemand()
+    {
+        WithWorkbook(
+            sheet =>
+            {
+                sheet.Cell(2, 1).Value = "Part 01";
+                sheet.Cell(2, 2).Value = 58;
+                sheet.Cell(3, 1).Value = "Skeleton";
+                sheet.Cell(3, 2).Value = 0;
+            },
+            path =>
+            {
+                var result = PartQuantityReader.Read(path);
+                Assert.Equal(58, result["Part 01"]);
+                Assert.Equal(0, result["Skeleton"]);
+                Assert.Equal(2, result.Count);
+            }
+        );
+    }
+
+    [Theory]
+    [InlineData("1.5")]
+    [InlineData("-1")]
+    [InlineData("NaN")]
+    [InlineData("")]
+    [InlineData("2147483648")]
+    public void RejectsInvalidQuantityInsteadOfDefaultingOrTruncating(string value)
+    {
+        WithWorkbook(
+            sheet =>
+            {
+                sheet.Cell(2, 1).Value = "Part";
+                sheet.Cell(2, 2).Value = value;
+            },
+            path => Assert.Throws<InvalidDataException>(() => PartQuantityReader.Read(path))
+        );
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void RejectsDuplicatePartsOrMissingQuantityHeader(bool duplicate)
+    {
+        WithWorkbook(
+            sheet =>
+            {
+                sheet.Cell(2, 1).Value = "Part";
+                sheet.Cell(2, 2).Value = 1;
+                if (duplicate)
+                {
+                    sheet.Cell(3, 1).Value = "Part";
+                    sheet.Cell(3, 2).Value = 2;
+                }
+                else
+                    sheet.Cell(1, 2).Value = "Unrecognized";
+            },
+            path => Assert.Throws<InvalidDataException>(() => PartQuantityReader.Read(path))
+        );
+    }
+
+    private static void WithWorkbook(Action<IXLWorksheet> prepare, Action<string> check)
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"opennest-quantities-{Guid.NewGuid()}.xlsx");
+        try
+        {
+            using (var workbook = new XLWorkbook())
+            {
+                var sheet = workbook.AddWorksheet("Parts");
+                sheet.Cell(1, 1).Value = "Part Name";
+                sheet.Cell(1, 2).Value = "Qty Required";
+                prepare(sheet);
+                workbook.SaveAs(path);
+            }
+            check(path);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+}