4 correct and re locate current mainpy logic

Moved testing logic from main.py in root path to proper tests in test_evaluators.py
created requirements for development with pytest library used in new test_evaluators.py
corrected requirements guidelines in README
added pytest usage to README
main.py now serves as uvicorn server launcher that runs app in app/routers/main.py
added routing to existing endpoints in app/routers/sessions.py via app/routers/main.py
corrected names in module .\services to evaluators.py and evaluators_factory.py

Bruno-val-bus / student-helper