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

.rubocop.yml

@@ -7,6 +7,7 @@ plugins:
 require:
   - ./rubocop/use_from_email.rb
   - ./rubocop/custom_cop_location.rb
+  - ./rubocop/attachment_download.rb
   - ./rubocop/one_class_per_file.rb
 
 Layout/LineLength:
@@ -41,6 +42,12 @@ Style/SymbolArray:
 Style/OpenStructUse:
   Enabled: false
 
+Chatwoot/AttachmentDownload:
+  Enabled: true
+  Exclude:
+    - 'spec/**/*'
+    - 'test/**/*'
+
 Style/OptionalBooleanParameter:
   Exclude:
     - 'app/services/email_templates/db_resolver_service.rb'