Add saveModuleToPKML() to serialize a MoBiModule

[PavelBal]

Summary

There is currently no way to serialize a MoBiModule back to a PKML file. loadModuleFromPKML() exists, but the reverse does not, so a module built or modified in R (e.g. via createMoBiModule() + extendInitialConditionsBB() / addProteinExpressionToParameterValuesBB()) cannot be persisted as a re-importable module.

What's missing

• R API: the PKML savers are saveInitialConditionsToPKML(), saveParameterValuesToPKML(), saveIndividualToPKML(), saveExpressionProfileToPKML(), saveDataSetToPKML(), and saveSimulation(). There is no saveModuleToPKML(), and the MoBiModule R6 object exposes no save method.

• .NET ModuleTask: exposes LoadModulesFromFile, CreateModule, AddBuildingBlocksToModule, RemoveBuildingBlockFromModule, the BB getters — but no ExportToPKML. A direct call throws:

  System.MissingMethodException: Could not find a suitable instance method ExportToPKML
  on type MoBi.R.Services.ModuleTask for method parameters Module, String
  

• Core persisters: only SimulationPersister (whole-simulation save) is available; there is no module/PKML persister for a single module.

Proposed

Add saveModuleToPKML(module, filePath) mirroring loadModuleFromPKML(path), backed by an ExportToPKML (or equivalent) method on the .NET ModuleTask, so that:

m <- loadModuleFromPKML(\"in.pkml\")
# ... modify m ...
saveModuleToPKML(m, \"out.pkml\")
identical_module <- loadModuleFromPKML(\"out.pkml\")

Use case

Workflows that programmatically build extension modules (e.g. adding a brain spatial-structure extension to PBPK models) want to persist the generated modules as standalone, re-importable PKML artifacts. Today the only workaround is saving each building block separately (saveInitialConditionsToPKML / saveParameterValuesToPKML), which loses the module wrapper.