Add gRPC client module and its corresponding test case

Client/Assets/Scripts/Test/GrpcClientTest.cs

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+using Network;
+using UnityEngine;
+
+namespace Test
+{
+    public class GrpcClientTest : MonoBehaviour
+    {
+        private async void Start()
+        {
+            var serverInfo = await GrpcClient.Instance.GetServerInfo();
+
+            Debug.Log($"Received info from server: {serverInfo}");
+
+            var loginResult = await GrpcClient.Instance.Login("野兽先辈", "114514");
+
+            Debug.Log($"Received login result: {loginResult.Result}");
+        }
+    }
+}

Client/Assets/Scripts/Test/GrpcClientTest.cs.meta

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+fileFormatVersion: 2
+guid: 98c1b145899d4d97bd981b177b5c45a9
+timeCreated: 1752478138