Add range validation for MCP::Annotations#priority per MCP specification

lib/mcp/annotations.rb

@@ -5,6 +5,8 @@ class Annotations
     attr_reader :audience, :priority, :last_modified
 
     def initialize(audience: nil, priority: nil, last_modified: nil)
+      raise ArgumentError, "The value of priority must be between 0 and 1." if priority && !priority.between?(0, 1)
+
       @audience = audience
       @priority = priority
       @last_modified = last_modified

test/mcp/annotations_test.rb

@@ -55,5 +55,31 @@ def test_initialization_with_last_modified_only
 
       assert_equal({ lastModified: timestamp }, annotations.to_h)
     end
+
+    def test_valid_priority_at_lower_bound
+      assert_nothing_raised do
+        Annotations.new(priority: 0)
+      end
+    end
+
+    def test_valid_priority_at_upper_bound
+      assert_nothing_raised do
+        Annotations.new(priority: 1)
+      end
+    end
+
+    def test_invalid_priority_above_upper_bound
+      exception = assert_raises(ArgumentError) do
+        Annotations.new(priority: 1.5)
+      end
+      assert_equal("The value of priority must be between 0 and 1.", exception.message)
+    end
+
+    def test_invalid_priority_below_lower_bound
+      exception = assert_raises(ArgumentError) do
+        Annotations.new(priority: -0.1)
+      end
+      assert_equal("The value of priority must be between 0 and 1.", exception.message)
+    end
   end
 end