import annotations from future for python <3.9

[sjoerd-bouma]

The type annotation list[str] in component_data.py (l.40) is not supported under Python versions <3.9.

This PR imports the required type annotation from __future__ so that it works on older Python versions also.

@telegraphic - would it be possible to make a single release (1.6.4) with this fix included? I think I would suggest to explicitly drop Python < 3.9 support for future versions (I'm happy to make a separate PR for that), so that pip install pygdsm will resolve correctly, but it would be nice to have one last stable release that also works on older versions (currently, pip install pygdsm will install 1.6.3 on python 3.7, which doesn't work).

[what-the-diff]

PR Summary

• Introduction of Future Import for Type Annotations
  The change includes an upgrade where we will now benefit from a feature called "type annotations". This essentially means our software will become more robust and less prone to potential issues thanks to improved code clarity and predictability. The developer team will now find it easier to understand the types of values that our software uses and produces.