Some pedantry: add `const` keywords where appropriate

[tuurep]

I have a habit of not using const which is probably not great, see for example:

https://www.reddit.com/r/C_Programming/comments/bg3bdq/comment/eli19si/

There's a concept called "const correctness" that basically means that variables should be declared "read only" (const, or constant) if they are indeed read-only. It's basically an additional type in the typing system, which lets the code and compiler help you make optimally-correct programs.

It can be a good exercise to go back to your code and find out where you can add const and where you can't.

Best to go through the whole code looking for these.