Move MCP::Annotations to its own file

Also, implement `Annotations#to_h`

Author: sambostock

lib/mcp.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require_relative "mcp/annotations"
 require_relative "mcp/configuration"
 require_relative "mcp/content"
 require_relative "mcp/instrumentation"
@@ -32,13 +33,4 @@ def configuration
       @configuration ||= Configuration.new
     end
   end
-
-  class Annotations
-    attr_reader :audience, :priority
-
-    def initialize(audience: nil, priority: nil)
-      @audience = audience
-      @priority = priority
-    end
-  end
 end

lib/mcp/annotations.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module MCP
+  class Annotations
+    attr_reader :audience, :priority
+
+    def initialize(audience: nil, priority: nil)
+      @audience = audience
+      @priority = priority
+
+      freeze
+    end
+
+    def to_h
+      { audience:, priority: }.compact.freeze
+    end
+  end
+end