fix: add namespaces to example executables

examples/BTCS_1D_proto_example.cpp

examples/BTCS_2D_proto_example.cpp

examples/CRNI_2D_proto_example.cpp

examples/FTCS_1D_proto_example.cpp

examples/FTCS_2D_proto_closed_mdl.cpp

examples/FTCS_2D_proto_example.cpp

examples/FTCS_2D_proto_example_mdl.cpp

examples/profiling_openmp.cpp

examples/profiling_speedup.cpp

examples/reference-FTCS_2D_closed.cpp