core: add grah i/o

1 job for gui in 57 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
failed build #34026

00:00:57

 
Name Stage Failure
failed
build Build
  586 | class dot_writer
| ^~~~~~~~~~
../lib/include/irritator/io.hpp:586:7: note: no known conversion for argument 1 from 'irt::simulation' to 'const irt::dot_writer&'
[15/18] Building CXX object app/gui/CMakeFiles/irritator-gui.dir/__/__/external/imgui/imgui_widgets.cpp.o
[16/18] Building CXX object app/gui/CMakeFiles/irritator-gui.dir/node-editor.cpp.o
ninja: build stopped: subcommand failed.
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1