Initial KV API concept

Core/Option/IOptionStorageAdapter.cs

@@ -0,0 +1,26 @@
+#nullable enable
+
+using System.Threading.Tasks;
+
+namespace Kruzya.TelegramBot.Core.Option;
+
+/// <summary>
+/// Implements an interaction with storage for options.
+/// </summary>
+public interface IOptionStorageAdapter
+{
+    /// <summary>
+    /// Loads a saved value (if exists) from storage.
+    /// </summary>
+    /// <param name="key"></param>
+    /// <returns></returns>
+    public Task<byte[]?> LoadValueAsync(IOptionKey key);
+
+    /// <summary>
+    /// Saves a passed value to storage.
+    /// </summary>
+    /// <param name="key">The unique chat key</param>
+    /// <param name="value">The serialized value for saving</param>
+    /// <returns></returns>
+    public Task SaveValueAsync(IOptionKey key, byte[] value);
+}