feat: added prepare obs to all the algorithms

[michele-milesi]

Summary

Describe the purpose of the pull request, including:

• Added a prepare_obs() function for each algorithm.
• The goal is to standardize the environment interaction for diambra submissions. We can keep it as an interim solution pending the handling of this aspect directly in the encoder.

EDIT:

• The process_obs function is used both during training and test.

Type of Change

Please select the one relevant option below:

• New feature (non-breaking change that adds functionality)

Checklist

Please confirm that the following tasks have been completed:

• I have tested my changes locally and they work as expected. (Please describe the tests you performed.)
• I have added unit tests for my changes, or updated existing tests if necessary.
• I have updated the documentation, if applicable.
• I have installed pre-commit and run locally for my code changes.