Introduce qlty

[Umekawa]

What

• Calculate and upload code coverage data to QLTY during CI
• Make code coverage and Maintainability viewable from the README

How

• Install simplecov_json_formatter
• Change the coverage output format to JSON
• Implement the coverage action from QLTY
• Add a badge to the README

Why

• The Code Climate API has been disabled
  • https://docs.qlty.sh/migration/guide

REF

• Remove codeclimate #194

[gemini-code-assist]

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[Copilot]

Pull Request Overview

This PR introduces Qlty as a replacement for Code Climate to handle code coverage reporting and maintainability metrics. The change migrates from Code Climate's deprecated API to Qlty's service.

• Configures SimpleCov to output JSON format coverage data
• Adds a new GitHub workflow job to upload coverage data to Qlty
• Updates README badges to display Qlty's maintainability and coverage metrics

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
spec/spec_helper.rb	Configures SimpleCov with JSON formatter and multi-format output
Gemfile	Adds simplecov_json_formatter dependency
.github/workflows/test.yml	Adds Qlty job for coverage upload
README.md	Updates badges to use Qlty metrics instead of Code Climate

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[kimkim0814]

This change is not related, but I was curious about the Travis CI part.
The diff looks LGTM!

[kimkim0814]

The current build status badge references Travis CI, but the actual CI environment has been migrated to GitHub Actions (see .github/workflows/test.yml.