feat(engine): introduce whole-job nesting contracts

OpenNest.Engine/Jobs/NestJob.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest;
+
+/// <summary>One material/unit system's requirements. Collections are copied; all nested values are immutable.</summary>
+public sealed class NestJob
+{
+    public NestJob(IEnumerable<NestJobPart> parts, IEnumerable<NestPlateStock> plates, NestJobOptions options = null)
+    {
+        Parts = Own(parts);
+        Plates = Own(plates);
+        Options = options ?? new NestJobOptions();
+        if (Parts.Select(p => p.Id).Distinct(StringComparer.Ordinal).Count() != Parts.Count ||
+            Plates.Select(p => p.Id).Distinct(StringComparer.Ordinal).Count() != Plates.Count)
+            throw new ArgumentException("Part and stock IDs must each be unique.");
+    }
+
+    public IReadOnlyList<NestJobPart> Parts { get; }
+    public IReadOnlyList<NestPlateStock> Plates { get; }
+    public NestJobOptions Options { get; }
+
+    internal static IReadOnlyList<T> Own<T>(IEnumerable<T> source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+        var values = source.ToArray();
+        if (values.Any(value => value is null))
+            throw new ArgumentException("Null entries are not allowed.", nameof(source));
+        return Array.AsReadOnly(values);
+    }
+}