Account Invoice Mass Sending

This module adds a background (asynchronous) way to email several invoices at once from the standard invoice sending wizard.

• In the invoice sending wizard, a new button "Email mass sending (Job Queue)" appears next to the normal send button. It is only visible when sending by email is selected and an email template is chosen.
• When you click it, the selected invoices are queued as background jobs and processed one by one, so Odoo does not freeze and each customer receives an individual email.
• A success notification tells you how many invoices will be processed in the background. If some invoices cannot be sent, a warning lists them: they are either already being processed or have no email address on the customer.
• On the invoice form, a "sending_in_progress" checkbox shows whether an invoice is currently being processed, which prevents sending the same invoice twice.
• The module relies on the Job Queue (queue_job) to run the sending in the background and defines its own job channel for these tasks.
• It extends the invoice model account.move and the sending wizard account.move.send.