Mark Node::Context as a long class

This is unfortunately rather long, but there doesn't seem any clear
single responsibility opportunities that can be embraced so I'm taking
the coward/assertive route of telling the linter: no.

lib/openapi3_parser/node/context.rb

@@ -14,6 +14,7 @@ module Node
     #                                                     node
     # @attr_reader  [Source::Location]  source_location   The location in a
     #                                                     source file of this
+    # rubocop:disable Metrics/ClassLength
     class Context
       # Create a context for the root of a document
       #
@@ -210,5 +211,6 @@ def openapi_version
         document.openapi_version
       end
     end
+    # rubocop:enable Metrics/ClassLength
   end
 end