We need a fixed time step main loop (https://gafferongames.com/post/fix_your_timestep/) with the following callbacks to an external game implementation:

• Init
• Cleanup
• FixedUpdate (with fixed dt)
• Update (unthrottled update)
• Render (unthrottled rendering)

• Make them into unique objects by creating some struct Assert##LINE##FILE as a tag for a templated assert class.
• Make them skippable if there is an ignore flag set on them (this shouldn't be possible for Asserts but just for warnings)

This issue requires some initialization and clean up code only

• bind key to action (either on/off or by using discrete values).
• see SDL_input for hi level api inspirations (https://github.com/TheJosh/SDL_input)

If the callback isn't set use std::err

Use std::err for the time being.

Keep the time as uint64 clocks but offer conversion utilities. See game engine architecture.