Expose server tool annotations on MCP::Client::Tool

Client#tools/#list_tools built Tool objects without an annotations
field even though the server includes annotations in every
tools/list response. Add the reader and pass the raw hash through,
mirroring how output_schema is already handled.

lib/mcp/client.rb

@@ -131,6 +131,7 @@ module MCP
           description: tool["description"],
           input_schema: tool["inputSchema"],
           output_schema: tool["outputSchema"],
+          annotations: tool["annotations"],
         )
       end
 

lib/mcp/client/tool.rb

@@ -3,13 +3,14 @@
 module MCP
   class Client
     class Tool
-      attr_reader :name, :description, :input_schema, :output_schema
+      attr_reader :name, :description, :input_schema, :output_schema, :annotations
 
-      def initialize(name:, description:, input_schema:, output_schema: nil)
+      def initialize(name:, description:, input_schema:, output_schema: nil, annotations: nil)
         @name = name
         @description = description
         @input_schema = input_schema
         @output_schema = output_schema
+        @annotations = annotations
       end
     end
   end