chore: Contact import improvements (#7787)

- Ensure existing contact information is updated on data import
- Refactor the existing job to make it more readable
- Fixes issues with import files in the wrong encoding
fixes: #7307

spec/mailers/administrator_notifications/channel_notifications_mailer_spec.rb

@@ -57,6 +57,24 @@ RSpec.describe AdministratorNotifications::ChannelNotificationsMailer do
     end
   end
 
+  describe 'contact_import_complete' do
+    let!(:data_import) { build(:data_import, total_records: 10, processed_records: 10) }
+    let(:mail) { described_class.with(account: account).contact_import_complete(data_import).deliver_now }
+
+    it 'renders the subject' do
+      expect(mail.subject).to eq('Contact Import Completed')
+    end
+
+    it 'renders the processed records' do
+      expect(mail.body.encoded).to match('Number of records imported: 10')
+      expect(mail.body.encoded).to match('Number of records failed: 0')
+    end
+
+    it 'renders the receiver email' do
+      expect(mail.to).to eq([administrator.email])
+    end
+  end
+
   describe 'contact_export_complete' do
     let!(:file_url) { Rails.application.routes.url_helpers.rails_blob_url(account.contacts_export) }
     let(:mail) { described_class.with(account: account).contact_export_complete(file_url).deliver_now }