fix: change validation for region statistics for by resvol constraint

[tjb-ltk]

Reservoir volume constraint needs region average quantities for computing fluid properties. The ave quantities are computed via tasks such as CompositionalMultiphaseStatistics (and SinglePhaseStatistics equivalent) that are triggered in event section
Previously validation attempted to check if compute statistics wrappers were present on region. This was incorrect. but maybe the region should own the statistics object.

New check looks at if region ave quantities are zero.

integrated tests are forthcoming..

[MelReyCG]

Maybe, to not expose the statistics component to the user, you can add in the well solver's registerDataOnMesh():

if( !wellControls.referenceReservoirRegion().empty() )
{
  // we need a statistics component for reference region pressure
  m_referenceRegionStats = taskManager.registerGroup<SinglePhaseStatistics>( "internalStats" )
    .setRestartFlags(NO_WRITE);
  m_referenceRegionStats.registerDataOnMeshRecursive(meshBodies);
}

m_referenceRegionStats would be a pointer or an std::optional, then you can call its execute() before reading it in updateVolRateForConstraint()

[MelReyCG]

We are testing the current state of the branch

[MelReyCG]

No success. I'll create a branch / PR on top of this one to contribute on this issue