fix: stream attachment handling in workers (#12870)

We’ve been watching Sidekiq workers climb from ~600 MB at boot to
1.4–1.5 GB after an hour whenever attachment-heavy jobs run. This PR is
an experiment to curb that growth by streaming attachments instead of
loading the whole blob into Ruby: reply-mailer inline attachments,
Telegram uploads, and audio transcriptions now read/write in chunks. If
this keeps RSS stable in production we’ll keep it; otherwise we’ll roll
it back and keep digging

spec/lib/integrations/slack/send_on_slack_service_spec.rb

@@ -206,6 +206,21 @@ describe Integrations::Slack::SendOnSlackService do
         expect(message.attachments.count).to eq 2
       end
 
+      it 'streams attachment blobs and uploads only once' do
+        expect(slack_client).to receive(:chat_postMessage).and_return(slack_message)
+
+        attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
+        attachment.file.attach(io: Rails.root.join('spec/assets/avatar.png').open, filename: 'avatar.png', content_type: 'image/png')
+        blob = attachment.file.blob
+        allow(blob).to receive(:open).and_call_original
+
+        expect(blob).to receive(:open).and_call_original
+        expect(slack_client).to receive(:files_upload_v2).once.and_return(file_attachment)
+
+        message.save!
+        builder.perform
+      end
+
       it 'handles file upload errors gracefully' do
         expect(slack_client).to receive(:chat_postMessage).with(
           channel: hook.reference_id,