Add ReCClient class and update project dependencies

Added `ReCClient` class to handle HTTP requests with JSON
serialization/deserialization support. Updated `ReC.Client.csproj`
to include `System.Net.Http` (v4.3.4) and `System.Text.Json`
(v9.0.11) as package references. Introduced conditional `using`
directives for `NETFRAMEWORK` compatibility.

src/ReC.Client/ReCClient.cs

@@ -0,0 +1,22 @@
+using System.Text.Json;
+#if NETFRAMEWORK
+using System;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+#else
+#endif
+
+namespace ReC.Client
+{
+    public class ReCClient
+    {
+        private readonly HttpClient _http;
+        private readonly JsonSerializerOptions _jsonOptions = new JsonSerializerOptions() { PropertyNameCaseInsensitive = true };
+
+        public ReCClient(HttpClient http)
+        {
+            _http = http ?? throw new ArgumentNullException(nameof(http));
+        }
+    }
+}