Reserve index 0 in SlotMap, improve unsafe collections

- Reserve index 0 as always invalid in SlotMap, ConcurrentSlotMap, UnsafeSlotMap, and UnsafeSparseSet; update all index checks and slot operations accordingly
- Refactor SlotMap to use parallel arrays and BitArray for occupancy
- Double capacity on resize for all major unsafe collections
- Add debugger display support for unsafe collections
- Improve NuGet publishing workflow to skip existing versions
- Increment package versions (LowLevel: 1.3.1, main: 1.0.2)
- Add comprehensive unit tests for SlotMap and ConcurrentSlotMap
- Update main program and documentation for new slot map behavior

Misaki.HighPerformance.Test/UnitTest/Collections/TestConcurrentSlotMap.cs

@@ -0,0 +1,60 @@
+using Misaki.HighPerformance.Collections;
+using System.Collections.Concurrent;
+
+namespace Misaki.HighPerformance.Test.UnitTest.Collections;
+
+[TestClass]
+public class TestSlotMap
+{
+    private SlotMap<int> _slotMap = null!;
+
+    [TestInitialize]
+    public void Initialize()
+    {
+        _slotMap = new SlotMap<int>();
+    }
+
+    [TestMethod]
+    public void TestDefaultIndex()
+    {
+        Assert.IsFalse(_slotMap.Contains(0, 0));
+    }
+
+    [TestMethod]
+    public void TestAddAndContains()
+    {
+        var slotIndex = _slotMap.Add(42, out var generation);
+        Assert.IsTrue(_slotMap.Contains(slotIndex, generation));
+        Assert.AreEqual(42, _slotMap.GetElementAt(slotIndex, generation));
+    }
+
+    [TestMethod]
+    public void TestRemove()
+    {
+        var slotIndex = _slotMap.Add(100, out var generation);
+        Assert.IsTrue(_slotMap.Contains(slotIndex, generation));
+        var removed = _slotMap.Remove(slotIndex, generation);
+        Assert.IsTrue(removed);
+        Assert.IsFalse(_slotMap.Contains(slotIndex, generation));
+    }
+
+    [TestMethod]
+    public void TestRemoveInvalid()
+    {
+        var slotIndex = _slotMap.Add(200, out var generation);
+        Assert.IsTrue(_slotMap.Contains(slotIndex, generation));
+        var removed = _slotMap.Remove(slotIndex, generation + 1); // Wrong generation
+        Assert.IsFalse(removed);
+        Assert.IsTrue(_slotMap.Contains(slotIndex, generation));
+    }
+
+    [TestMethod]
+    public void TestIndexReuse()
+    {
+        var slotIndex1 = _slotMap.Add(300, out var generation1);
+        _slotMap.Remove(slotIndex1, generation1);
+        var slotIndex2 = _slotMap.Add(400, out var generation2);
+        Assert.AreEqual(slotIndex1, slotIndex2);
+        Assert.AreNotEqual(generation1, generation2);
+    }
+}