[#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/IClientStatus.cs

@@ -0,0 +1,28 @@
+namespace FrostFS.SDK.ClientV2;
+
+public interface IClientStatus
+{
+    // isHealthy checks if the connection can handle requests.
+    bool IsHealthy();
+
+    // isDialed checks if the connection was created.
+    bool IsDialed();
+
+    // setUnhealthy marks client as unhealthy.
+    void SetUnhealthy();
+
+    // address return address of endpoint.
+    string Address { get; }
+
+    // currentErrorRate returns current errors rate.
+    // After specific threshold connection is considered as unhealthy.
+    // Pool.startRebalance routine can make this connection healthy again.
+    uint GetCurrentErrorRate();
+
+    // overallErrorRate returns the number of all happened errors.
+    ulong GetOverallErrorRate();
+
+    // methodsStatus returns statistic for all used methods.
+    StatusSnapshot[] MethodsStatus();
+}
+