Move self methods into self block

app/services/group_stage_service.rb

@@ -1,7 +1,8 @@
 # frozen_string_literal: true
 
 class GroupStageService
-  def self.generate_group_stage(groups)
+  class << self
+    def generate_group_stage(groups)
       raise 'Cannot generate group stage without groups' if groups.length.zero?
 
       # raise an error if the average group size is not a whole number
@@ -11,11 +12,11 @@ class GroupStageService
       Stage.new level: -1, groups: groups
     end
 
-  def self.get_group_object_from(team_array)
+    def get_group_object_from(team_array)
       Group.new matches: generate_all_matches_between(team_array)
     end
 
-  def self.generate_all_matches_between(teams)
+    def generate_all_matches_between(teams)
       matches = []
       teams.combination(2).to_a # = matchups
            .each_with_index do |matchup, i|
@@ -30,3 +31,4 @@ class GroupStageService
       matches
     end
   end
+end