✨ Add `appraisal`

[pboling]

• test Matrix:
  • [ [Rails 6.1, 7.0, 7.1, 7.2, 8.0] x [Ruby 3.0, 3.1, 3.2, 3.3, 3.4] ]
• loosen rubocop dep requirements
• upgrade dependencies
• lint updates
• upgrade to actions/checkout@v4
• add rubocop-packaging
• fixes undeclared dependency on rubocop-factory_bot by adding it
• allow rubocop-rspec v3
• prefer YAML.safe_load_file

Replaces #63, #60

[pboling]

@smudge This is ready for review!, let me know if you'd like anything split into a separate PR.