Introduce the foundational setup for the Kuwait payroll localization, serving as the base for subsequent enhancements, and implement core legal requirements including Social Security, End of Service (EOS), and leave logic.

The goal of this change is to establish a functional payroll framework compliant with Kuwait Labor Law. It provides a consistent baseline by:
1. Setting up demo data and standard working schedules for immediate testing.
2. Automating Social Security calculations for employee deductions and company contributions.
3. Implementing complex End of Service indemnity logic based on service duration and departure reasons (e.g., resignation tiers).
4. Handling specific leave computations, including tiered deductions for sick leave and monthly provisions for accounting accuracy.

Technical summary:
- Added demo company: "My Kuwaiti Company" and linked employees.
- Defined standard working schedule (9:00–17:00, Sunday–Thursday).
- Introduced Kuwait salary structure "Kuwait: Monthly Pay".
- Added Rule Parameters for Social Security:
  - Basic Pension: Employee (10%), Company (15%).
  - Unemployment: Employee (0.5%), Company (0.5%).
- Added Salary Rules for:
  - Social Security deductions and contributions.
  - End of Service Benefit: Logic for "Resigned" (<3y: 0%, 3-5y: 50%, 5-10y: 66%, >10y: 100%), "Fired" (0%), and standard calculation (15 days/year first 5 years, 1 month thereafter).
  - End of Service Provision: Monthly accrual calculation.
  - Annual Leave Provision and Remaining Leaves Compensation.
- Added "Kuwait Annual Leaves" Accrual Plan (2.5 days/month, starts after 6 months) and linked it to the Annual Leave type.
- Overridden `_get_worked_day_lines` in `hr.payslip` to implement tiered deduction logic for Sick Leaves (15 days full pay, 10 days 75%, etc.).

task-5116274