Add custom JSONSchemer::Schema#inspect

The default `inspect` method hangs for some large schemas (eg,
`JSONSchemer.openapi31_document`) for some reason. This seems like
something that should be fixed in Ruby generally, but it is what it is.

lib/json_schemer/schema.rb

@@ -231,6 +231,10 @@ def error(formatted_instance_location:, **)
       "instance at #{formatted_instance_location} does not match schema"
     end
 
+    def inspect
+      "#<#{self.class.name} @value=#{@value.inspect} @parent=#{@parent.inspect} @keyword=#{@keyword.inspect}>"
+    end
+
   private
 
     def parse

test/json_schemer_test.rb

@@ -289,6 +289,12 @@ def test_draft7_additional_items_error
     assert_equal('array items at root do not match `additionalItems` schema', OutputHelper.as_json!(schemer.validate([1, 2])).dig('errors', 1, 'error'))
   end
 
+  def test_inspect
+    output = JSONSchemer.openapi31_document.inspect
+    assert_includes(output, 'JSONSchemer::Schema')
+    assert_includes(output, '@value=')
+  end
+
   def test_it_allows_validating_schemas
     valid_draft7_schema = { '$ref' => '#/definitions/~1some~1%7Bid%7D' }
     invalid_draft7_schema = { '$ref' => '#/definitions/~1some~1{id}' }