HR Expense Advance Clearing Sequence

This module makes Odoo use a separate numbering series for employee advance expense reports, so they can be told apart from normal expense reports.

• A new sequence is installed with the prefix AV and four digits (for example AV0001).
• When a new expense report is created and it is an advance (or is created from an advance context), Odoo automatically fills in its reference number from this advance sequence.
• If the sequence cannot produce a number, the reference is left as a simple slash.
• Normal expense reports that are not advances keep using the standard numbering from the related expense sequence module.

The change is applied on the expense report model hr.expense.sheet, so it works wherever expense reports are created in Odoo, including the Expense app. No new menus, buttons or reports are added; the only visible difference for users is the reference number shown on advance expense reports.