Enable RuboCop Minitest and RuboCop Rake for development

Based on the following information, `rubocop-minitest` and `rubocop-rake` have been added
for development. Autocorrection has been applied for offenses detected by `rubocop-minitest`.

```console
$ bundle exec rake
(snip)

Running RuboCop...
Inspecting 40 files
........................................

40 files inspected, no offenses detected

Tip: Based on detected gems, the following RuboCop extension libraries might be helpful:
* rubocop-minitest (https://rubygems.org/gems/rubocop-minitest)
* rubocop-rake (https://rubygems.org/gems/rubocop-rake)

You can opt out of this message by adding the following to your config
(see https://docs.rubocop.org/rubocop/extensions.html#extension-suggestions for more options):
AllCops:
    SuggestExtensions: false
```

If preserving the existing behavior is preferred, it is also possible to set `SuggestExtensions: false`.

test/model_context_protocol/tool/input_schema_test.rb

@@ -25,7 +25,7 @@ module ModelContextProtocol
 
       test "missing_required_arguments returns an empty array if no required arguments are missing" do
         input_schema = InputSchema.new(properties: { message: { type: "string" } }, required: [:message])
-        assert_equal [], input_schema.missing_required_arguments({ message: "Hello, world!" })
+        assert_empty input_schema.missing_required_arguments({ message: "Hello, world!" })
       end
     end
   end