feat(sva): date calculator service for a dossier and a procedure

app/services/sva_svr_date_calculator_service.rb

@@ -0,0 +1,23 @@
+class SVASVRDateCalculatorService
+  attr_reader :dossier, :procedure
+
+  def initialize(dossier, procedure)
+    @dossier = dossier
+    @procedure = procedure
+  end
+
+  def calculate
+    config = procedure.sva_svr_configuration
+    unit = config.unit.to_sym
+    period = config.period.to_i
+
+    case unit
+    when :days
+      dossier.depose_at.to_date + period.days
+    when :weeks
+      dossier.depose_at.to_date + period.weeks
+    when :months
+      dossier.depose_at.to_date + period.months
+    end
+  end
+end