build: Improve dev setup

Gemfile

@@ -2,6 +2,12 @@
 
 source 'https://rubygems.org'
 
+def eval_version(dependency, version)
+  return [dependency] if version.empty?
+
+  version.count('.') < 2 ? [dependency, "~> #{version}.0"] : [dependency, version]
+end
+
 if ENV['DEVEL'] == '1'
   gem 'activeadmin_quill_editor', path: './'
 else
@@ -9,20 +15,22 @@ else
 end
 
 ruby_ver = ENV.fetch('RUBY_VERSION', '')
-rails_ver = ENV.fetch('RAILS_VERSION', '')
-activeadmin_ver = ENV.fetch('ACTIVEADMIN_VERSION', '')
 
-rails = rails_ver.empty? ? ['rails'] : ['rails', "~> #{rails_ver}"]
+rails_ver = ENV.fetch('RAILS_VERSION', '')
+rails = eval_version('rails', rails_ver)
 gem(*rails)
 
-activeadmin = activeadmin_ver.empty? ? ['activeadmin'] : ['activeadmin', "~> #{activeadmin_ver}"]
-gem(*activeadmin)
+active_admin_ver = ENV.fetch('ACTIVEADMIN_VERSION', '')
+active_admin = eval_version('activeadmin', active_admin_ver)
+gem(*active_admin)
 
-ruby32 = Gem::Version.new(ruby_ver) >= Gem::Version.new('3.2')
-rails72 = Gem::Version.new(rails_ver) >= Gem::Version.new('7.2')
-sqlite3 = ruby32 || rails72 ? ['sqlite3'] : ['sqlite3', '~> 1.4']
+ruby32 = ruby_ver.empty? || Gem::Version.new(ruby_ver) >= Gem::Version.new('3.2')
+rails72 = rails_ver.empty? || Gem::Version.new(rails_ver) >= Gem::Version.new('7.2')
+sqlite3 = ruby32 && rails72 ? ['sqlite3'] : ['sqlite3', '~> 1.4']
 gem(*sqlite3)
 
+gem 'zeitwerk', '~> 2.6.18' unless ruby32
+
 # NOTE: to avoid error: uninitialized constant ActiveSupport::LoggerThreadSafeLevel::Logger
 gem 'concurrent-ruby', '1.3.4'