### Issue:
When creating a subscription with several lines whose quantities add up to zero, the next invoice date is not updated and set to the start date.

### Steps to reproduce:
- Install 'sale_subscription'
- Create a new Subscription with two lines and a tart data several months in the past
- One with a quantity of 1 and a higher price
- The other with a quantity of -1
- It can be the same service product with invoicing based on ordered quantity
- Confirm the Subscription
- Click "Create Invoice" and confirm the invoice
- Back to the Subscription, the next invoice date was not updated.

### Cause:
In `_get_max_invoiced_date()` to compute the invoiced periods we check the quantity corresponding to this period. But if an invoice has two lines with opposite quantities, they will cancel each other out at this line:

https://github.com/odoo/enterprise/blob/c2ac44f492ec53083864f07ff5bfbff9458ddf2a/sale_subscription/models/account_move_line.py#L131

So the method will return not return the date in `invoice_dates`.

Later, if `_get_max_invoiced_date()` returns nothing for `last_invoice_end_date` then `next_invoice_date` is set to `start_date`:

https://github.com/odoo/enterprise/blob/c2ac44f492ec53083864f07ff5bfbff9458ddf2a/sale_subscription/models/account_move.py#L66-L67

### Solution:
The goal was to not include invoices that were fully refunded for the `last_invoice_end_date`. This is why `_get_max_invoiced_date()` substract the quantities from refunds.

To make this work we can take the absolute value of the quantity returned by the compute method before giving it the wanted sign based on if it's an invoice or a refund.

opw-5360930

Forward-Port-Of: odoo/enterprise#106226
Forward-Port-Of: odoo/enterprise#103705

Currently, an error occurs while generating a payslip for an employee who is linked to more than one commission plan using the same payslip input.

**Steps to Reproduce:**
1. Install the hr_payroll_sale_commission module.
2. Create a user and link to an employee. Set a contract for the employee.
3. Create two commission plans for the same user:
   - Use the same Payslip Input in both plans.
   - Set the Target Frequency to "Monthly" for both.
4. Generate a payslip for the employee.

Ref: [Video](https://drive.google.com/file/d/1HhtUL2xznS_Aoi9ePL0OJLdGaXU8ZFZR/view?usp=sharing)

**Error:**
`ValueError - Expected singleton: sale.commission.report(30026010100009, 40026010100009)`

**Cause:**
When multiple commission records belong to the same payslip input, it tries to convert the commission amount using `coms.commission`, where coms has multiple recordsets. This leads to a singleton error during currency conversion.

**Fix:**
This commit ensures the currency conversion is applied per commission and prevents the singleton error.

sentry-7187854690

Forward-Port-Of: odoo/enterprise#104600
Forward-Port-Of: odoo/enterprise#104464