[yuri-zubov]

This pull request updates the *.gemspec file to optimize the gem package size and structure

$ gem build -o before.tar.gz

$ git switch reduce-gem-size

$ gem build -o after.tar.gz

$ du -sh before.tar.gz after.tar.gz
 16K	before.tar
 12K	after.tar
 

	before	after	saved
size	16K	12K	-4K (⏷ -25%)

whitch files was deleted?

data
-├── .github
-│   └── workflows
-│       └── ci.yml
-├── bin
-│   ├── console
-│   └── setup
-├── gemfiles
-│   ├── .bundle
-│   │   └── config
-│   ├── rails_6.1.gemfile
-│   ├── rails_7.0.gemfile
-│   ├── rails_7.1.gemfile
-│   ├── rails_7.2.gemfile
-│   ├── rails_8.0.gemfile
-│   └── rails_edge.gemfile
 ├── lib
 │   ├── database_cleaner
 │   │   ├── active_record
 │   │   │   ├── base.rb
 │   │   │   ├── deletion.rb
 │   │   │   ├── transaction.rb
 │   │   │   ├── truncation.rb
 │   │   │   └── version.rb
 │   │   └── active_record.rb
 │   └── database_cleaner-active_record.rb
-├── tmp
-│   └── .keep
-├── .gitignore
-├── .rspec
-├── Appraisals
 ├── CHANGELOG.md
-├── CONTRIBUTE.md
-├── database_cleaner-active_record.gemspec
-├── docker-compose.db.yml
-├── docker-compose.yml
-├── Dockerfile
-├── Gemfile
 ├── LICENSE.txt
-├── Rakefile
 └── README.md

ps: you can see on rails repo