change to forward reference for possibly unbound symbols in type hint(s)

[pantheraleo-7]

merge after #101 is merged.

based on #101(comment)

[pantheraleo-7]

Just realised, this is present in many libraries. An automated patch might be a better approach than manual PRs.

Automating quoting the symbols might be error prone, so adding this import should do the [same] job:
from __future__ import annotations

This enables lazy evaluation of type annotations in Python 3.7+

[FoamyGuy]

using from __future__ import annotations might be easier than trying to update things to use quoted references. I think we added that as an import in the core that exists to make it compatible with that behavior.

We can try searching in the bundle to find ones that have this stuff in the except block of their guarded typing import.

[pantheraleo-7]

The PR on INA219 is required because it removes the I2C = None thing. But this PR becomes optional, as I2C = None already got removed by #101, if you intend to include the from __future__ import annotations import via an automated script/method.

[FoamyGuy]

We can merge this now, and still consider a more broad solution down the line.

Thanks for contributing!