[FIX] point_of_sale: properly reconcile receivable lines

Description of the issue/feature this PR addresses:
Fixes an error raised by #84827

Current behavior before PR:
The following error was found

Add the option Print invoices on customer requeston a Pos Config.
Open a session
Create 2 orders for the same customer and invoice them
Return one of the orders and invoice it
Two account moves will have amount_residual != 0 (the credit note and one of the orders) (tested on runbot)

Desired behavior after PR is merged:

The result is that all moves are reconciled.

In order to not loose it, I added tests for this issue and the issue fixed on #84827

closes odoo/odoo#86656

X-original-commit: c66d708a
Signed-off-by: Grazioso Andrea (agr) <agr@odoo.com>