you know, all foundations will crack to an extent and some more than others.
Your third sentence should probably read, there are NOT any cracks in the walls. Am I correct???
What your fixing to do does concern me, because my leadership would be to keep an eye on it and see what happens. If it gets worse, you need to fix it, BUT covering it with wood flooring will forever hide it from observations Tough call.
I would also install that special floating stretchable membrane that is installed over cracks in foundations when laying down vinyl tile, flooring of wood, and others. This will keep the wood from buckling and moving around over this crack.
You can now officially consider this crack in the foundation your new expansion joint. It will move around with the seasons.
Cracks are normal, and the treatment is to watch them.