FIX: dropping cached_properties functionality

[Gui-FernandesBR]

Pull request type

Please check the type of change your PR introduces:

• Code maintenance (refactoring, formatting, renaming, tests)

Pull request checklist

• Code base maintenance (refactoring, formatting, renaming):

  • Docs have been reviewed and added / updated if needed
  • Lint (black rocketpy) has passed locally and any fixes were made
  • All tests (pytest --runslow) have passed locally

What is the current behavior?

cached_properties were introduced by #249 , but apperantly this functionality is available only on python 3.8 or higher.
As Google Colaboratory currently applies python 3.7 as default, we think it's not a good time to drop python 3.7 support.

What is the new behavior?

Simple search and replace @cached_property --> @property @functools.lru_cache()

Does this introduce a breaking change?

• Yes
• No

Other information

This only happened cause the github tests were seted to run using python 3.8, which was fixed by #262

[Gui-FernandesBR]

• Google Colab worked as expected (use !pip install git+https://github.com/RocketPy-Team/RocketPy.git@maint/drop_cached_properties_use to reproduce);
• Tests are running and passing locally,

I think we are ready for review !!

[giovaniceotto]

Please elaborate on the differences between @cached_property and @functools.lru_cache.

What are the benefits of @cached_property?

[giovaniceotto]

@Gui-FernandesBR, please see #283

[Gui-FernandesBR]

#283 already seems better in my opinion. I am closing this PR but will keep the branch for a while. If needed, we can easily re-open.

Thank you @giovaniceotto for helping!