[#24] Client: Implement pool part1

first iteration - base classes and methods

Signed-off-by: Pavel Gross <p.gross@yadro.com>

src/FrostFS.SDK.ClientV2/Poll/WorkList.cs

@@ -0,0 +1,26 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace FrostFS.SDK.ClientV2;
+
+internal sealed class WorkList
+{
+    private readonly List<int> elements = [];
+
+    internal int Length
+    {
+        get { return elements.Count; }
+    }
+
+    internal void Add(int element)
+    {
+        elements.Add(element);
+    }
+
+    internal int Remove()
+    {
+        int last = elements.LastOrDefault();
+        elements.RemoveAt(elements.Count - 1);
+        return last;
+    }
+}