feat: add is_carrying_minerals field for Unit class

Every unit has now a field is_carrying_minerals that will return True if the unit holds minerals, False otherwise.

python-api-src/lib_unit.cpp

@@ -34,6 +34,7 @@ void define_unit(py::module & m)
         .def_property_readonly("current_ability_id", &Unit::getCurrentAbilityID, "The AbilityID of currently used ability")
         .def_property_readonly("facing", &Unit::getFacing)
         .def_property_readonly("radius", &Unit::getRadius)
+        .def_property_readonly("is_carrying_minerals", &Unit::isCarryingMinerals)
         .def("hold_position", &Unit::holdPosition)
         .def("patrol", py::overload_cast<const CCPosition &>(&Unit::patrol, py::const_))
         .def("stop_dance", &Unit::stopDance)