Remove deprecated size_t overloads from RigActiveCellInfo

Migrate all callers to use type-safe ReservoirCellIndex and
ActiveCellIndex wrappers, then remove the deprecated isActive(size_t),
cellResultIndex(size_t), and setCellResultIndex(size_t, size_t) methods.

ApplicationLibCode/ReservoirDataModel/Well/RigAccWellFlowCalculator.cpp

@@ -41,7 +41,7 @@ size_t RigEclCellIndexCalculator::resultCellIndex( size_t gridIndex, size_t grid
 {
     size_t reservoirCellIndex = m_mainGrid->reservoirCellIndexByGridAndGridLocalCellIndex( gridIndex, gridCellIndex );
 
-    return m_activeCellInfo->cellResultIndex( reservoirCellIndex );
+    return m_activeCellInfo->cellResultIndex( ReservoirCellIndex( reservoirCellIndex ) ).value();
 }
 
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