Fix typing for redis

[lzchen]

Followup to #3110

I believe Pep 0604 which introduces union typing syntax is only supported for Python 3.10+. Since all instrumentations still support 3.8+, I believe we still need to adhere to the explicit Optional and Union typings.

[Kludex]

@lzchen This is not needed.

The from __future__ import annotations on the first line makes sure Python will not look at the type hints at runtime - Which allow us to use type hints from more modern versions.

Also... The pipeline for Python 3.8 and 3.9 is passing... 😅

[samuelcolvin]

@lzchen this change is not necessary.

As of pep-0563 introduced in Python 3.7, the magic import

from __future__ import annotations

causes Python to not evaluate type hints, this in turn means we can use new syntax like | unions even with older versions of Python. Static type checkers like mypy and pyright can still read and interpret these type annotations, so there's no drawback.

Many popular python packages like Pydantic, FastAPI, rich, cryptography use this technique.

Even Microsoft (who I believe you work for) make extensive use of from __future__ import annotations to adopt modern typing while supporting older versions of python:

In the most downloaded python package from Microsoft azure-core, there are 82 references to from __future__ import annotations, indeed azure-sdk-for-python/doc/dev /static_type_checking.md includes this:

*Note: Supported in Python 3.9+. For <3.9, You must include from __future__ import annotations import to be able to pass in generic list[str] as a type hint rather than typing.List[str].