account_invoice_start_end_dates

Introduces configurable start and end date tracking on invoice lines with validations driven by product settings.

Key Features

account.move.line: Adds start and end date fields to invoice journal items and displays them on invoice line forms and lists.
account.move.line: Validates that start and end dates are both present, chronologically ordered, and required when date-mandatory products are posted.
product.template: Adds a Must Have Start/End Dates option so products can mandate date entry on their invoice lines.
account.move: Shows start and end date columns on invoice line grids for direct editing during invoice preparation.
account.invoice.report: Extends the invoice analysis report with start and end date columns for reporting.