bugfix for duplicate symbols

[pmocz]

Fixes issue: #80

The issue is that:

According to the cpp standard, an explicit instantiation is only allowed to appear once in the entire program.

https://en.cppreference.com/w/cpp/language/class_template

Some gcc compilers will fail if this is not the case.

The challenge is that the member functions of the templated classes have been defined in multiple files (engine_run.cpp, engine_printer.cpp, engine_init.cpp, engine_step_report.cpp). The solution is to only explicitly instantiate the class in engine_init.cpp and then only instantiate rest of the functions in the other files.

See:

https://stackoverflow.com/questions/21534435/separate-compilation-and-template-explicit-instantiation

[haykh]

@pmocz thanks Philip! kinda weird that with clang19 this warning doesn't show up :\ also, yes, this is one of the reasons i hate c++ so much. in any other language you wouldn't even have to instantiate it at all. the compiler should be able to deduce that from places where the class is used. will merge it to the new release candidate instead of master.