FIX: optional imports for EnvironmentAnalysis prevent default install.

[phmbressan]

Pull request type

Please check the type of change your PR introduces:

• Code base additions (bugfix, features)
• Code maintenance (refactoring, formatting, renaming, tests)
• ReadMe, Docs and GitHub maintenance
• Other (please describe):

Pull request checklist

Please check if your PR fulfills the following requirements, depending on the type of PR:

• Code base additions (for bug fixes / features):

  • Tests for the changes have been added
  • 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?

The default rocketpy install through pip does not install the optional dependencies as intended. However, importing the package loaded the EnvironmentAnalysis module that required them, raising an error.

What is the new behavior?

The imports of the optional modules are made lazily, i.e. on instantiation of an EnvironmentAnalysis object. Then, the expected install behavior is assured.

Does this introduce a breaking change?

• Yes
• No

Other information

The way the imports were done goes against PEP8 convention of only handling imports in top level statements. However, the implemented way is simpler for just these few dependencies. In the long term, if more complex install conditions are needed, an file to process this requirements (as in pandas repository) may be considered.

[MateusStano]

I believe we are still missing changes on the imports of environment_analysis_plots.py and environment_analysis_prints.py for this PR to work