Cleanup leftovers in packages_dependencies table

What does this MR do and why?

MR !20549 (merged) added two tables: packages_dependencies and packages_dependency_links. When a package is deleted, packages_dependency_links rows are properly deleted but rows in packages_dependencies are kept and they can become orphans. This MR aims to clean up those orphaned packages_dependencies records.

How to set up and validate locally

1. In Rails console, create a bunch of orphaned packages_dependencies records: FactoryBot.create_list(:packages_dependency, 100)
2. Enable the feature flag : Feature.enable(:packages_delete_orphaned_dependencies_worker)
3. Run the cleanup sidekiq worker: Packages::Cleanup::DeleteOrphanedDependenciesWorker.perform_async, the orphaned records should be deleted.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Database analysis

1. !113076 (comment 1297596269)
2. !113076 (comment 1322050386)

Related to #38266 (closed)

app/models/packages/dependency.rb

 # frozen_string_literal: true
 class Packages::Dependency < ApplicationRecord
+  include EachBatch
+
   has_many :dependency_links, class_name: 'Packages::DependencyLink'
 
   validates :name, :version_pattern, presence: true
@@ -9,6 +11,7 @@ class Packages::Dependency < ApplicationRecord
   NAME_VERSION_PATTERN_TUPLE_MATCHING = '(name, version_pattern) = (?, ?)'
   MAX_STRING_LENGTH = 255
   MAX_CHUNKED_QUERIES_COUNT = 10
+  BATCH_SIZE = 3000
 
   def self.ids_for_package_names_and_version_patterns(names_and_version_patterns = {}, chunk_size = 50, max_rows_limit = 200)
     names_and_version_patterns.reject! { |key, value| key.size > MAX_STRING_LENGTH || value.size > MAX_STRING_LENGTH }
@@ -41,6 +44,17 @@ def self.pluck_ids_and_names
     pluck(:id, :name)
   end
 
+  def self.orphaned
+    subquery = Packages::DependencyLink.where(Packages::DependencyLink[:dependency_id].eq(Packages::Dependency[:id]))
+    where_not_exists(subquery)
+  end
+
+  def self.delete_orphaned_in_batches(batch_size: BATCH_SIZE)
+    orphaned.each_batch(of: batch_size) do |relation| # rubocop:disable Style/SymbolProc
+      relation.delete_all
+    end
+  end
+
   def orphaned?
     self.dependency_links.empty?
   end