Include hidden users in stats

If users participated and were hidden after participating, we should
still count them in the participants stats.

In the tests, we set users' `hidden_at` attribute before they vote.
Although in real life they would vote first and then they would be
hidden, I've written the tests like this for the sake of simplicity.

app/models/concerns/statisticable.rb

@@ -34,7 +34,7 @@ module Statisticable
     end
 
     def participants
-      User.where(id: participant_ids)
+      User.unscoped.where(id: participant_ids)
     end
 
     def total_male_participants

spec/models/budget/stats_spec.rb

@@ -7,10 +7,10 @@ describe Budget::Stats do
 
   describe "#participants" do
     let(:author) { investment.author }
-    let(:author_and_voter) { create(:user) }
+    let(:author_and_voter) { create(:user, hidden_at: Time.current) }
     let(:voter) { create(:user) }
     let(:voter_and_balloter) { create(:user) }
-    let(:balloter) { create(:user) }
+    let(:balloter) { create(:user, hidden_at: Time.current) }
     let(:poll_balloter) { create(:user, :level_two) }
     let(:non_participant) { create(:user, :level_two) }
 
@@ -29,7 +29,7 @@ describe Budget::Stats do
       create(:poll_voter, :from_booth, user: non_participant, budget: create(:budget))
     end
 
-    it "returns unique participants, including authors" do
+    it "returns unique participants, including authors and hidden users" do
       expect(stats.participants).to match_array(
         [author, author_and_voter, voter, voter_and_balloter, balloter, poll_balloter]
       )

spec/models/poll/stats_spec.rb

@@ -4,6 +4,15 @@ describe Poll::Stats do
   let(:poll) { create(:poll) }
   let(:stats) { Poll::Stats.new(poll) }
 
+  describe "#participants" do
+    it "includes hidden users" do
+      create(:poll_voter, poll: poll)
+      create(:poll_voter, poll: poll, user: create(:user, :level_two, hidden_at: Time.current))
+
+      expect(stats.participants.count).to eq(2)
+    end
+  end
+
   describe "total participants" do
     before { allow(stats).to receive(:total_web_white).and_return(1) }