Add and apply Performance/Sum rubocop rule

We're not adding it for performance reasons but because it simplifies
the code.

.rubocop.yml

@@ -217,6 +217,9 @@ Performance/EndWith:
 Performance/StartWith:
   Enabled: true
 
+Performance/Sum:
+  Enabled: true
+
 Rails/ActiveRecordCallbacksOrder:
   Enabled: true
 

app/models/budget/stats.rb

@@ -54,7 +54,7 @@ class Budget::Stats
   end
 
   def total_votes
-    budget.ballots.pluck(:ballot_lines_count).reduce(0) { |sum, x| sum + x }
+    budget.ballots.pluck(:ballot_lines_count).sum
   end
 
   def total_selected_investments
@@ -72,18 +72,18 @@ class Budget::Stats
     end
 
     groups[:total] = Hash.new(0)
-    groups[:total][:total_investments_count] = groups.map { |_k, v| v[:total_investments_count] }.sum
+    groups[:total][:total_investments_count] = groups.sum { |_k, v| v[:total_investments_count] }
-    groups[:total][:total_participants_support_phase] = groups.map { |_k, v| v[:total_participants_support_phase] }.sum
+    groups[:total][:total_participants_support_phase] = groups.sum { |_k, v| v[:total_participants_support_phase] }
-    groups[:total][:total_participants_vote_phase] = groups.map { |_k, v| v[:total_participants_vote_phase] }.sum
+    groups[:total][:total_participants_vote_phase] = groups.sum { |_k, v| v[:total_participants_vote_phase] }
-    groups[:total][:total_participants_every_phase] = groups.map { |_k, v| v[:total_participants_every_phase] }.sum
+    groups[:total][:total_participants_every_phase] = groups.sum { |_k, v| v[:total_participants_every_phase] }
 
     budget.headings.each do |heading|
       groups[heading.id].merge!(calculate_heading_stats_with_totals(groups[heading.id], groups[:total], heading.population))
     end
 
-    groups[:total][:percentage_participants_support_phase] = groups.map { |_k, v| v[:percentage_participants_support_phase] }.sum
+    groups[:total][:percentage_participants_support_phase] = groups.sum { |_k, v| v[:percentage_participants_support_phase] }
-    groups[:total][:percentage_participants_vote_phase] = groups.map { |_k, v| v[:percentage_participants_vote_phase] }.sum
+    groups[:total][:percentage_participants_vote_phase] = groups.sum { |_k, v| v[:percentage_participants_vote_phase] }
-    groups[:total][:percentage_participants_every_phase] = groups.map { |_k, v| v[:percentage_participants_every_phase] }.sum
+    groups[:total][:percentage_participants_every_phase] = groups.sum { |_k, v| v[:percentage_participants_every_phase] }
 
     groups
   end

app/models/legislation/process.rb

@@ -110,7 +110,7 @@ class Legislation::Process < ApplicationRecord
   end
 
   def total_comments
-    questions.sum(:comments_count) + draft_versions.map(&:total_comments).sum
+    questions.sum(:comments_count) + draft_versions.sum(&:total_comments)
   end
 
   def status

lib/remote_translations/microsoft/sentences_parser.rb

@@ -18,6 +18,6 @@ module RemoteTranslations::Microsoft::SentencesParser
   end
 
   def characters_count(texts)
-    texts.map(&:size).reduce(:+)
+    texts.sum(&:size)
   end
 end

lib/tasks/proposal_actions.rake

@@ -384,7 +384,7 @@ namespace :proposal_actions do
       5
     ]
 
-    votes_count = expected_supports.reduce(0.0) { |sum, x| sum + x }
+    votes_count = expected_supports.sum
     goal_votes = Setting["votes_for_proposal_success"].to_f
     cached_votes_up = 0