Payment Counterpart Lines Import XLSX

This module adds an Excel import for the distribution (counterpart) lines of a payment. On a payment in draft state, a new button "Import Payment Distribution" appears next to the "Reset to Draft" button. It opens an Excel import wizard using the template "Payment Distribution (import)" (file payment_detail.xlsx).

The template expects columns for description, invoice/move, amount, account, analytic account and fully paid. When the file is imported, the module:

• Deletes the existing counterpart lines of the payment before loading the new ones.
• Fills missing descriptions with "/".
• If an invoice number is given, replaces it with the invoice name and uses the invoice partner.
• If no account is given, uses the payment's destination account code.
• Adds the payment partner when a column is missing.

After import, a post-processing step recalculates each line from its linked journal entry (move) and then restores the imported description and amount, so the lines stay consistent with the accounting entry.

The module works on account.payment and its counterpart lines (line_payment_counterpart_ids), and relies on the Excel import/export framework.