Add templates for setters and getters

[jcurtis2]

Attempting to simplify code by introducing templates for setting and getting of attributes and derived values.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.21%. Comparing base (f924d65) to head (efdc266).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #464      +/-   ##
==========================================
+ Coverage   91.04%   91.21%   +0.16%     
==========================================
  Files          55       56       +1     
  Lines        2636     2618      -18     
  Branches      144      144              
==========================================
- Hits         2400     2388      -12     
+ Misses        163      157       -6     
  Partials       73       73              

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[Griger5]

Maybe it would be beneficial to "abstract" the templates even more? get_value and set_value look the same in env_state.hpp and aero_particle.hpp. Maybe we could do something like this in a separate header (named getters.hpp ?):

namespace pypartmc { // possible namespace to avoid name conflicts

template <typename T, typename SelfType, typename Func>
inline T get_value(const SelfType &self, Func func) { // inline to keep it header-only
    T value{};
    func(self.ptr.f_arg(), &value);
    return value;
}

template <typename T, typename SelfType, typename Func>
inline void set_value(SelfType &self, Func func, T value) {
    func(self.ptr.f_arg_non_const(), &value);
}

}

And an example call would look like:

static auto get_height(const EnvState &self) {
     return pypartmc::get_value<double>(self, f_env_state_get_height);
}

The same could be considered for get_derived_value and get_derived_value_env_state. I'm not sure if these ones have a lot of uses in other classes, but even if they do not now, they could do in the future!