How to install a wall-safe in a concrete wall?
The simplest and most efficient method is to add a new wall, and have the safe in place when you pour it.

Barring that, for a "really, I'm QUITE sure it's not structural" wall, rental or purchase of various destructive technologies will aid the process - diamond core drills can make large holes cleanly and quickly. Diamond saw blades can make grooves between holes (few will make it through the entire wall thickness, and those would be hard to manage anyway) or for a cruder approach various levels of jackhammer-related tooling (hammer-drills at the low end, actual jackhammers that are a bit much to manage on a wall at the high end) will bash out concrete and/or drill holes somewhat faster than regular drills but more crudely than core drills. Presumably you'll pour new concrete (or grout) around the safe when in place, so crude may not matter much, so long as you don't knock the whole wall down.