Add type hints to main.py and server.py

[PhilWun]

This PR adds type hints to function declarations and some variables in main.py and server.py to improve the development experience.

[github-actions[bot]]

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[mcmonkey4eva]

For ease of review & merge, could you please separate these? No more than one file at a time to have this type of bulk formatting

Especially since these are such core files being edited, by the time a review can happen, fresh merge conflicts inevitably appear, so it needs to be kept small at a time to dodge that