`LoadSimulationsFromSnapshot()` does not return population simulations

[Felixmil]

If a pop sim is defined in a snapshot, the loadSimulationsFromSnapshot() function will return a simulations object that does not include population simulations.

To be expected because populations are supposed to be passed to the populations argument of runSimulations but this should be explicitly described somewhere (or improved ?).

[rwmcintosh]

Improved. I think we can link together a few issues in PKSim and OSPSuite.R to make this feature a lot better for users.

[rwmcintosh]

Design notes — resolve this by carrying the population on the loaded simulation (rather than documenting the separate-arg workaround)

Root cause. LoadSimulationsFromSnapshot maps each PK-Sim Simulation → IModelCoreSimulation via SimulationToModelCoreSimulationMapper, which carries only Model + Configuration + name/creation/id. It has no population concept, so a PopulationSimulation's IndividualValuesCache and AgingData are dropped — the returned R Simulation is the base individual. (Confirmed in PKSim.R.Services.SnapshotTask.coreSimulationFrom → the mapper at OSPSuite.Core SimulationToModelCoreSimulationMapper.MapFrom.)

Fix (agreed approach). Instead of documenting that populations must go through the separate population argument, preserve the population on the returned simulation object so a loaded population simulation runs as a population. This is enabled by OSPSuite.Core adding two peer properties to OSPSuite.R.Domain.Simulation (IndividualValuesCache + AgingData) — see Open-Systems-Pharmacology/OSPSuite.Core#2896.

PK-Sim side (this issue) — in PKSim.R.Services.SnapshotTask: when the source PK-Sim simulation is a PopulationSimulation, populate the new wrapper properties:

• IndividualValuesCache — build the complete per-individual cache = the population's IndividualValuesCache plus the simulation-level advanced parameters. Mirror what IPopulationExportTask.CreatePopulationDataFor(PopulationSimulation) does (it merges population.IndividualValuesCache + populationSimulation.AllAdvancedParameters(...) via AllValuesFor), but target an IndividualValuesCache rather than a DataTable.
  • ⚠️ Grabbing the bare populationSimulation.Population.IndividualValuesCache would silently drop advanced parameters (PopulationSimulation.ParameterValuesCache is documented as not containing the underlying population's distributed parameters). Must merge.
• AgingData — flatten the PK-Sim AgingData.AllParameterData (per-parameter IndividualIndexes/Times/Values lists) into the OSPSuite.R.Domain.AgingData arrays (IndividualIds/ParameterPaths/Times/Values). Read from AllParameterData raw (not PK-Sim's ToDataTable(), which quotes the parameter path) to stay consistent with the R aging path.

The reference implementation already exists: PopulationSimulationEngine.RunAsync extracts exactly populationData (via CreatePopulationDataFor) + AgingData.ToDataTable() when running a pop sim.

Blocking order: blocked by Open-Systems-Pharmacology/OSPSuite.Core#2896 (the wrapper properties); consumed by Open-Systems-Pharmacology/OSPSuite-R#1981 (the runSimulations consolidation that lets a mixed list of loaded individual + population simulations run in one call).