Prefer require_relative for internal requires

`require_relative` is preferred over `require` for files within the same
project because it uses paths relative to the current file, making code
more portable and less dependent on the load path.

This change updates internal requires to use `require_relative` for
consistency, performance, and improved portability.

Retain `require` for dynamic paths in `lib/slim_lint.rb` because they
use absolute paths.

Refs:
- rubocop/rubocop#8748
- sds/haml-lint#521

lib/slim_lint.rb

@@ -6,37 +6,37 @@
 # Need to load slim before we can reference some classes or define filters
 require 'slim'
 
-require 'slim_lint/constants'
-require 'slim_lint/exceptions'
-require 'slim_lint/configuration'
-require 'slim_lint/configuration_loader'
-require 'slim_lint/utils'
-require 'slim_lint/atom'
-require 'slim_lint/sexp'
-require 'slim_lint/file_finder'
-require 'slim_lint/linter_registry'
-require 'slim_lint/logger'
-require 'slim_lint/version'
+require_relative 'slim_lint/constants'
+require_relative 'slim_lint/exceptions'
+require_relative 'slim_lint/configuration'
+require_relative 'slim_lint/configuration_loader'
+require_relative 'slim_lint/utils'
+require_relative 'slim_lint/atom'
+require_relative 'slim_lint/sexp'
+require_relative 'slim_lint/file_finder'
+require_relative 'slim_lint/linter_registry'
+require_relative 'slim_lint/logger'
+require_relative 'slim_lint/version'
 
 # Load all filters (required by SlimLint::Engine)
 Dir[File.expand_path('slim_lint/filters/*.rb', File.dirname(__FILE__))].sort.each do |file|
   require file
 end
 
-require 'slim_lint/engine'
-require 'slim_lint/document'
-require 'slim_lint/capture_map'
-require 'slim_lint/sexp_visitor'
-require 'slim_lint/lint'
-require 'slim_lint/ruby_parser'
-require 'slim_lint/linter'
-require 'slim_lint/reporter'
-require 'slim_lint/report'
-require 'slim_lint/linter_selector'
-require 'slim_lint/runner'
+require_relative 'slim_lint/engine'
+require_relative 'slim_lint/document'
+require_relative 'slim_lint/capture_map'
+require_relative 'slim_lint/sexp_visitor'
+require_relative 'slim_lint/lint'
+require_relative 'slim_lint/ruby_parser'
+require_relative 'slim_lint/linter'
+require_relative 'slim_lint/reporter'
+require_relative 'slim_lint/report'
+require_relative 'slim_lint/linter_selector'
+require_relative 'slim_lint/runner'
 
 # Load all matchers
-require 'slim_lint/matcher/base'
+require_relative 'slim_lint/matcher/base'
 Dir[File.expand_path('slim_lint/matcher/*.rb', File.dirname(__FILE__))].sort.each do |file|
   require file
 end

lib/slim_lint/cli.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require 'slim_lint'
-require 'slim_lint/options'
+require_relative '../slim_lint'
+require_relative 'options'
 
 module SlimLint
   # Command line application interface.

lib/slim_lint/linter/rubocop.rb

@@ -1,7 +1,8 @@
 # frozen_string_literal: true
 
-require 'slim_lint/ruby_extractor'
-require 'slim_lint/ruby_extract_engine'
+require_relative '../ruby_extractor'
+require_relative '../ruby_extract_engine'
+
 require 'rubocop'
 
 module SlimLint

lib/slim_lint/rake_task.rb

@@ -2,7 +2,8 @@
 
 require 'rake'
 require 'rake/tasklib'
-require 'slim_lint/constants'
+
+require_relative 'constants'
 
 module SlimLint
   # Rake task interface for slim-lint command line interface.
@@ -74,8 +75,8 @@ def define
 
       task(name, [:files]) do |_task, task_args|
         # Lazy-load so task doesn't affect Rakefile load time
-        require 'slim_lint'
-        require 'slim_lint/cli'
+        require_relative '../slim_lint'
+        require_relative 'cli'
 
         run_cli(task_args)
       end