Test: fix SVA decision date when start date is at end of month and with correction delay

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[what-the-diff]

PR Summary

• Adjustment in Decision Date Calculation Method
  The logic behind our decision date calculation has been improved in app/services/sva_svr_decision_date_calculator_service.rb. The way we add the duration and delay corrections together has been modified. This is aimed at more accuracy in our operations.

• Setup For Procedure Processing Job Tests
  A new setup routine has been added in spec/jobs/procedure_sva_svr_process_dossier_job_spec.rb. Essentially, what this does is pre-set a specific date for when travel time calculation tests are being conducted. This will ensure more consistent and reliable testing results.

• Enhancements in Decision Date Calculator Tests
  Our testing procedures for the decision date calculation processes have been expanded in spec/services/sva_svr_decision_date_calculator_service_spec.rb. These new tests ensure that the decision date is calculated correctly based on different starting dates and the number of days in various months. This helps us validate our decision date calculation logic with a suite of different scenarios and conditions to ensure our calculations are correct regardless of the circumstances.