Add ToolAnnotations support (#124)

* Add ToolAnnotations support

* Address feedback

src/ModelContextProtocol/Protocol/Types/ToolAnnotations.cs

@@ -0,0 +1,54 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Additional properties describing a Tool to clients.
+/// NOTE: all properties in ToolAnnotations are **hints**.
+/// They are not guaranteed to provide a faithful description of tool behavior (including descriptive properties like `title`).
+/// Clients should never make tool use decisions based on ToolAnnotations received from untrusted servers.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
+/// There are multiple subtypes of content, depending on the "type" field, these are represented as separate classes.
+/// </summary>
+public class ToolAnnotations
+{
+    /// <summary>
+    /// A human-readable title for the tool.
+    /// </summary>
+    [JsonPropertyName("title")]
+    public string? Title { get; set; }
+
+    /// <summary>
+    /// If true, the tool may perform destructive updates to its environment.
+    /// If false, the tool performs only additive updates.
+    /// (This property is meaningful only when <see cref="ReadOnlyHint"/> is false).
+    /// Default: true.
+    /// </summary>
+    [JsonPropertyName("destructiveHint")]
+    public bool? DestructiveHint { get; set; }
+
+    /// <summary>
+    /// If true, calling the tool repeatedly with the same arguments 
+    /// will have no additional effect on its environment.
+    /// (This property is meaningful only when <see cref="ReadOnlyHint"/> is false).
+    /// Default: false.
+    /// </summary>
+    [JsonPropertyName("idempotentHint")]
+    public bool? IdempotentHint { get; set; }
+
+    /// <summary>
+    /// If true, this tool may interact with an "open world" of external entities.
+    /// If false, the tool's domain of interaction is closed.
+    /// For example, the world of a web search tool is open, whereas that of a memory tool is not.
+    /// Default: true.
+    /// </summary>
+    [JsonPropertyName("openWorldHint")]
+    public bool? OpenWorldHint { get; set; }
+
+    /// <summary>
+    /// If true, the tool does not modify its environment.
+    /// Default: false.
+    /// </summary>
+    [JsonPropertyName("readOnlyHint")]
+    public bool? ReadOnlyHint { get; set; }
+}