By Mexican labor law, employees are entitled to at least one paid rest day per week (commonly known as the Seventh Day). Depending on the contract, some schedules provide two rest days.

There are two ways to pay this concept:
* Fixed amount: The employee receives the full daily salary regardless of absences (already supported).
* Prorated amount: Applies strictly to weekly and 14-days schedule pays. The payment is proportional to the actual time worked during the period (new feature).

The prorated seventh day is calculated using the following formula: `accrued_days * work_rate * daily_salary`

Where:
* Accrued days: Actual days/hours worked in the period.
* Work rate: A proportional factor based on the rest days and working days per week: `rest_days / working_days_per_week`. Rest days are dynamically calculated using the `hours_per_day` and `hours_per_week` fields from the `resource_calendar_id`.
* Daily salary: Retrieved from the `l10n_mx_daily_salary` field.

EXAMPLE 1: WEEKLY SCHEDULE WITH 1 REST DAY
For a wage of 7,000 MXN weekly (daily wage = 1,000 MXN), the rate is `1/6 = 0.16666`.
The payment depends on the worked days:

| Worked Days | Seventh Day Amount Paid            |
| ----------- | ---------------------------------- |
| 1           | 1 * 0.16666 * 1,000 =   166.67 MXN |
| 2           | 2 * 0.16666 * 1,000 =   333.33 MXN |
| 3           | 3 * 0.16666 * 1,000 =   500.00 MXN |
| 4           | 4 * 0.16666 * 1,000 =   666.67 MXN |
| 5           | 5 * 0.16666 * 1,000 =   833.33 MXN |
| 6           | 6 * 0.16666 * 1,000 = 1,000.00 MXN |

EXAMPLE 2: WEEKLY SCHEDULE WITH 2 REST DAYS
For the same daily wage, but with a 5-day workweek, the rate is 2/5 = 0.4.

| Worked Days | Seventh Day Amount Paid          |
| ----------- | -------------------------------- |
| 1           | 1 * 0.40000 * 1,000 =   400.00 MXN |
| 5           | 5 * 0.40000 * 1,000 = 2,000.00 MXN |

* Add test_cfdi_nomina_con_septimo_dia test

target: master
task-5259458