Estimate employment dates

Estimate the first and last day each employee worked and was employed. The estimate comes from payroll data, not from hire or termination dates. Pay periods on approved or paid payrolls set the range, ignoring historical payrolls and corrections. estimated_first_day_worked and estimated_last_day_worked ignore $0 pay stubs. estimated_first_day_employed and estimated_last_day_employed also count $0 pay stubs that record hours, such as unpaid leave. A pay rate that starts inside the first pay period moves the first day later, and a pay rate that ends inside the last pay period moves the last day earlier.