Step 1 — Replace SharedPrimitive scalar fields with plain C++ types across all interface classes

[Andrea-Havron-NOAA]

Labels: refactor, C++

Parent: #1644

Note: PopulationInterface has already been migrated as a reference implementation (see PR #N). This issue covers the remaining interface classes.

In every interface class, replace SharedInt, SharedBoolean, SharedReal, and SharedString fields that hold scalar configuration values with their plain C++ equivalents (int, bool, double, std::string). This is only safe to do in conjunction with Step 3 (removal of constructor copies), because without the copy there is no synchronization problem to solve.

Files to update

• rcpp_fleet.hpp — SharedInt data ID fields, SharedString name, SharedString observed_units
• rcpp_recruitment.hpp — SharedInt n_years, SharedInt process_id, SharedReal estimated values
• rcpp_growth.hpp — SharedInt n_years
• rcpp_data.hpp — SharedInt amax, SharedInt ymax in data interface classes
• rcpp_distribution.hpp — SharedString input_type_m, SharedString use_mean_m, SharedInt interface_observed_data_id_m, SharedString notes
• For each class: remove SharedPrimitive field declarations, add plain-type equivalents with sensible defaults, update all .get() / .set() call sites, and update add_to_fims_tmb_internal() accordingly.