Feat: Make MAPElitesRepertoire more modular so that it can store any kind of information.

[Lookatator]

Depends on this previous PR: #209
Related issue: #191

Make MAPElitesRepertoire more modular so that it can store any kind of information.

Changes:

• Standardizes extra_scores handling across all repertoire classes by:
  • Adding keys_extra_scores parameter to control which extra scores are stored
  • Adding filter_extra_scores method to filter extra scores based on keys
  • Updating add() and init() methods to properly handle extra scores
• Moves observations from being a dedicated field (in UnstructuredRepertoire) to being stored in extra_scores
• Updates AURORA class and Seq2seq training to use the new extra_scores interface

Motivation

• Reduces code duplication by unifying handling of extra scores across repertoire implementations
• Makes the codebase more maintainable by standardizing how additional evaluation data is stored
• Allows for more flexible storage of additional data beyond just observations (e.g. age of individuals, number of addition to a cell...)

Technical Details

• Added filter_extra_scores method to GARepertoire base class
• Updated initialization and add methods across repertoire classes to properly handle extra_scores

Checks

• a clear description of the PR has been added
• sufficient tests have been written
  N/A relevant section added to the documentation
  N/A example notebook added to the repo
• clean docstrings and comments have been written
• if any issue/observation has been discovered, a new issue has been opened