[Large] Fix Python type annotations

[MarcellPerger1]

There are currently many new type warnings in the code as Pycharm's typechecker got a lot stricter in the last update.
Therefore, we need to change/improve the types in many parts of the codebase to not have these warnings.

• parser.common
• parser.lexer
• parser.cst
• parser.astgen
• parser.typecheck
• util
• test.common
• test/coverage/inject_colors.py
• test.test_common
• test.test_tokenizer
• test.test_cstgen
• test.test_astgen
• test.test_typechecker
• test.test_e2e