[#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/Statistic.cs

@@ -0,0 +1,12 @@
+using System.Collections.ObjectModel;
+
+namespace FrostFS.SDK.ClientV2;
+
+public sealed class Statistic
+{
+    public ulong OverallErrors { get; internal set; }
+
+    public Collection<NodeStatistic> Nodes { get; } = [];
+
+    public string[]? CurrentNodes { get; internal set; }
+}