fix: Error shouldn't halt the campaign for entire audience (#11980)

## Summary
- handle Twilio failures per contact when running one-off SMS campaigns
- rescue errors in WhatsApp and generic SMS one-off campaigns so they
continue
- add specs confirming campaigns continue sending when a single contact
fails

fixes:  https://github.com/chatwoot/chatwoot/issues/9000

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/services/sms/oneoff_sms_campaign_service.rb

@@ -29,5 +29,7 @@ class Sms::OneoffSmsCampaignService
 
   def send_message(to:, content:)
     channel.send_text_message(to, content)
+  rescue StandardError => e
+    Rails.logger.error("[SMS Campaign #{campaign.id}] Failed to send to #{to}: #{e.message}")
   end
 end