Add type hints

[Greyvend]

When running mypy on the code that uses flaky, you get:

Skipping analyzing 'flaky': found module but no type hints or library stubs

Here is how it can be fixed.

[ssbarnea]

Untyped decorator makes function "test_prerun_reqs_v1" untyped

Can we please add type hints to flaky? Its a shame not to have type hints for a QA tool ;)