Cache unwrap and to_type_signature on type wrappers

Type wrappers (NonNull, List) are schema-level immutable objects whose
unwrap and to_type_signature results never change. Memoize both to
eliminate repeated recursive unwrap calls and string allocations during
validation and introspection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: swalkinshaw

lib/graphql/schema/list.rb

@@ -19,7 +19,7 @@ def list?
       end
 
       def to_type_signature
-        "[#{@of_type.to_type_signature}]"
+        @type_signature ||= -"[#{@of_type.to_type_signature}]"
       end
 
       # This is for introspection, where it's expected the name will be `null`

lib/graphql/schema/non_null.rb

@@ -24,7 +24,7 @@ def list?
       end
 
       def to_type_signature
-        "#{@of_type.to_type_signature}!"
+        @type_signature ||= -"#{@of_type.to_type_signature}!"
       end
 
       def inspect

lib/graphql/schema/wrapper.rb

@@ -13,7 +13,13 @@ def initialize(of_type)
       end
 
       def unwrap
-        @of_type.unwrap
+        @unwrapped ||= @of_type.unwrap
+      end
+
+      def freeze
+        unwrap
+        to_type_signature
+        super
       end
 
       def ==(other)