Add type hints to some variables

[nikhilwoodruff]

This helps IDEs like VS Code recognise and suggest class properties.

New features

• Add type hints for all instances of variable_name in function declarations.
• Add type hints for some Simulation and Population properties.

[nikhilwoodruff]

Hmm, there's a lot of unexpected issues here.

[MattiSG]

Indeed! I suggest you focus on the results of make lint, which you can run locally for faster feedback 🙂

[bonjourmauko]

Weirdly the status checks do not seem to run on our side.