Add type hints to `test_base.py` (#2445)

Add type hints to `test_base.py` (#2445)

* added type annotations to test-base.py

* deleted unused imports

* fixed import order

* conditional import

* conditional import TestClient on types.py

* using string literals when importing in types

* added missing imports

* deleted starlette/types, refactored test_base types

* deleted types

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Co-authored-by: Scirlat Danut <scirlatdanut@scirlats-mini.lan>
Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>