Enhance JobScheduler and related classes

Added XML documentation comments to the `JobScheduler` class and its methods.
Added a new method `GetJobStatus` in the `JobScheduler` class for job status retrieval.
Added a new `CollectionHandle` struct for collection management.
Added a new test class `TestUnsafeSparseSet` with unit tests for `UnsafeSparseSet`.

Changed the `WorkerThread` class to improve job retrieval logic with a new `FindJob` method.
Changed the `DynamicArena` class by removing commented-out code to streamline memory management.

Removed commented-out code in the `WorkerThread` class for improved readability.
Removed the `ArenaAllocator` struct from `AllocationManager` to clean up unused code.
Removed the `ParallelWriter` struct from `UnsafeSparseSet`, indicating a shift in handling sparse sets.

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

@@ -0,0 +1,46 @@
+using Misaki.HighPerformance.LowLevel.Buffer;
+using Misaki.HighPerformance.LowLevel.Collections;
+
+namespace Misaki.HighPerformance.Test.UnitTest.Collections;
+
+[TestClass]
+public class TestUnsafeSparseSet
+{
+    private UnsafeSparseSet<int> _sparseSet;
+
+    [TestInitialize]
+    public void Initialize()
+    {
+        _sparseSet = new UnsafeSparseSet<int>(16, Allocator.Persistent);
+    }
+
+    [TestMethod]
+    public void Add()
+    {
+        var id = _sparseSet.Add(10);
+        Assert.IsTrue(_sparseSet.Contains(id));
+    }
+
+    [TestMethod]
+    public void Remove()
+    {
+        var id = _sparseSet.Add(20);
+        Assert.IsTrue(_sparseSet.Contains(id));
+
+        _sparseSet.Remove(id);
+        Assert.IsFalse(_sparseSet.Contains(id));
+    }
+
+    [TestMethod]
+    public void IndexReuse()
+    {
+        var id = _sparseSet.Add(20);
+        Assert.IsTrue(_sparseSet.Contains(id));
+
+        _sparseSet.Remove(id);
+        Assert.IsFalse(_sparseSet.Contains(id));
+
+        var newId = _sparseSet.Add(30);
+        Assert.AreEqual(id, newId);
+    }
+}