Subpopulation categories are now user-defined from
population_data$initialization; non-reserved columns are
detected automatically.
Improved checkpoint restore behavior in
parse_config(): when restore_from is provided,
population_data$initialization can be used as mapping-only
metadata (without N, S0, I0,
etc.).
Improved validation messages for category filters: invalid category names now list available categories, and invalid category values now list valid values for the selected category.
Improved format_metarvm_output() handling of
population_id and dynamic column selection for user-defined
categories.
Updated documentation and vignettes to reflect user-defined subpopulation categories and checkpoint restore behavior.