fix linting issues

[rei-moo]

Inspired by #558 with the addition of disabling Lint/RedundantCopDisableDirective in .rubocop.yml in order to prevent rubocop errors related to unknown cops for Ruby versions 2.7 and prior.

[Copilot]

Pull request overview

This PR fixes linting issues to comply with rubocop-github standards, inspired by PR #558. The changes include updating .rubocop.yml to use plugins: instead of require: for rubocop-performance, disabling Lint/RedundantCopDisableDirective for Ruby 2.7 compatibility, and removing several cop disables that are now consistently enforced across all supported Ruby versions.

Key changes:

• Standardized class method definitions from class << self blocks to def self.method_name syntax
• Added consistent spacing inside hash literal braces ({ key: value } instead of {key: value})
• Replaced conditional assignment pattern from unless modifier to ||= operator
• Updated .rubocop.yml to disable Lint/RedundantCopDisableDirective while enabling previously disabled style cops

Reviewed changes

Copilot reviewed 13 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.rubocop.yml	Changed require: to plugins: for rubocop-performance, removed previously disabled cops, added Lint/RedundantCopDisableDirective disable
spec/spec_helper.rb	Converted class << self to def self. syntax for test helper methods
spec/lib/secure_headers_spec.rb	Added spaces inside hash literal braces throughout test cases
spec/lib/secure_headers/middleware_spec.rb	Added spaces inside hash literal braces for cookie configuration tests
spec/lib/secure_headers/headers/policy_management_spec.rb	Fixed let (:default_opts) to let(:default_opts)
spec/lib/secure_headers/headers/cookie_spec.rb	Added spaces inside hash literal braces for cookie test configurations
spec/lib/secure_headers/headers/content_security_policy_spec.rb	Fixed let (:default_opts) and added spaces inside hash literal braces
spec/lib/secure_headers/configuration_spec.rb	Added spaces inside hash literal braces for configuration tests
lib/secure_headers/headers/x_xss_protection.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/x_permitted_cross_domain_policies.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/x_frame_options.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/x_download_options.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/x_content_type_options.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/strict_transport_security.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/referrer_policy.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/expect_certificate_transparency.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/cookie.rb	Converted class << self to def self. syntax
lib/secure_headers/headers/clear_site_data.rb	Converted class << self to def self. syntax
lib/secure_headers.rb	Changed conditional assignment from unless modifier to `

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[fletchto99]

✅ lint changes look good!