v(3.3.4) - NormalizeObservation calibration load improvement

[AlejandroCN7]

Description

This PR enhances the loading of previous normalization calibrations for model evaluations. It now allows specifying paths to txt files generated by Sinergym.

Additionally, this patch includes improved checks and error messages when performing these loads.

Motivation and Context

• [ ] I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (update in the documentation)
• [x] Improvement (of an existing feature)
• [ ] Others

Checklist:

• [ ] I've read the CONTRIBUTION guide (required)
• [ ] My change requires a change to the documentation.
• [ ] I have updated the tests.
• [x] I have updated the documentation accordingly.
• [ ] I have reformatted the code using autopep8 second level aggressive.
• [ ] I have reformatted the code using isort.
• [ ] I have ensured cd docs && make spelling && make html pass (required if documentation has been updated.)
• [ ] I have ensured pytest tests/ -vv pass. (required).
• [ ] I have ensured pytype -d import-error sinergym/ pass. (required)

Changelog:

• NormalizeObservation Wrapper: Added txt path file option in constructor.
• Unified len mean and var assert, use the same checks in setters.
• Update documentation and drl notebook with this functionality

Extra:

• Included some get_wrapper_attr in sinergym tests.