Implement getMolWeightFor() to work with Quantity

[rengelke]

getMolWeightFor() retrieves the molecular weight of a quantity's (parent) molecule, returning it in the specified unit.
Returns NA if no molecule is found, or throws an error if stopIfNotFound = TRUE.

Utilizes helper .getParentContainerByType which allows to get the parent container of a quantity by type.

Closes #1500

[PavelBal]

@Felixmil @rwmcintosh I forgot how it works now with the core files - they are updated automatically? Should they be part of the PR?

[Felixmil]

@Felixmil @rwmcintosh I forgot how it works now with the core files - they are updated automatically? Should they be part of the PR?

Yes, they are retrieved from latest pksim build and commit to the PR's branch by a github action:

[rengelke]

@Felixmil @rwmcintosh I forgot how it works now with the core files - they are updated automatically? Should they be part of the PR?

Yes, they are retrieved from latest pksim build and commit to the PR's branch by a github action

Just learned that there will be a problem pulling the core files when the package is loaded

[Felixmil]

Just learned that there will be a problem pulling the core files when the package is loaded

Yes, because they are in use. Restarting the R session is necessary. We should also update the update_core_files.R script to restart the session before running it.

[rengelke]

Just learned that there will be a problem pulling the core files when the package is loaded

Yes, because they are in use. Restarting the R session is necessary. We should also update the update_core_files.R script to restart the session before running it.

Sure, makes sense to restart, but one might not consider it during the first time.

Just learned that there will be a problem pulling the core files when the package is loaded

Yes, because they are in use. Restarting the R session is necessary. We should also update the update_core_files.R script to restart the session before running it.

Yes, makes sense to restart before pulling the core files while working on the PR. But Do I miss something - how is changing update_core_files.R going to help as this is used in the context of the GitHub action.