Modernize dependencies and fix CI

[dduugg]

Summary

CI uses the shared workflow at rubyatscale/shared-config/.github/workflows/ci.yml, which tests against Ruby 3.2, 3.3, and 3.4. Several gems in the lock file were incompatible with Ruby 3.4, causing bundle install to fail.

Dependency updates:

• Fix Ruby 3.4 CI failure: nokogiri-1.16.4-x86_64-linux has a hard constraint of < 3.4.dev; updated to 1.19.1
• Update all outdated gems: rails 7.0 → 8.1, rubocop 1.45 → 1.85, sorbet/tapioca 0.5/0.7 → 0.6/0.17, packwerk 2.2 → 3.2, rack 2 → 3, and many more
• Bump bundler to 4.0.7
• Remove git-sourced packwerk override from Gemfile — no longer needed now that packwerk 3 is on RubyGems
• Bump packwerk dependency in gemspec from >= 2.2.1 to >= 3, consistent with the README
• Bump required_ruby_version in gemspec from >= 2.7 to >= 3.2 to match the lowest Ruby version tested in CI

Sorbet/Tapioca:

• Regenerate all tapioca RBI files for updated gem versions
• Regenerate rdoc RBI under Ruby 4.0 to fix type check failure

Linting:

• Add rubocop-gusto as a development dependency and plugin in .rubocop.yml
• Autocorrect 62 rubocop offenses (rubocop -a)
• Generate .rubocop_todo.yml for remaining 73 violations

Fixes https://github.com/rubyatscale/packwerk-extensions/actions/runs/22682101326

[dkisselev]

As a fast-follow it could be worth letting claude take a pass through resolving/minimizing as many of these as we can.

[dkisselev]

🎉