Configure SimpleCov to generate JSON coverage for qlty

Add simplecov-json formatter to generate coverage.json file that qlty
requires for coverage tracking in CI.

Changes:
- Add simplecov-json gem dependency
- Configure multi-formatter in CI to generate both HTML and JSON
- JSON coverage only generated in CI environment to avoid local overhead

This enables qlty to properly track test coverage metrics in GitHub Actions.

Author: voltechs

registry.gemspec

@@ -30,5 +30,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rspec_junit_formatter', '~> 0.6'
   spec.add_development_dependency 'rubocop', '~> 1.50'
   spec.add_development_dependency 'simplecov', '~> 0.22'
+  spec.add_development_dependency 'simplecov-json', '~> 0.2'
   spec.add_development_dependency 'benchmark-ips', '~> 2.10'
 end

spec/spec_helper.rb

@@ -3,10 +3,19 @@
 require 'pry'
 
 require 'simplecov'
+require 'simplecov-json'
 
 Dir['./spec/support/**/*.rb'].each { |f| require f }
 SimpleCov.start do
   add_filter 'spec'
+
+  # Generate both HTML and JSON formats for qlty
+  if ENV['CI']
+    formatter SimpleCov::Formatter::MultiFormatter.new([
+      SimpleCov::Formatter::HTMLFormatter,
+      SimpleCov::Formatter::JSONFormatter
+    ])
+  end
 end
 
 require 'registry'