Remove pandas implementation from the repository

[adamamer20]

We have decided to deprecate the pandas-based implementation to fully focus on the polars backend, which has proven to scale significantly better and offers superior performance.

Removing pandas references will:

• Simplify the codebase
• Enhance maintainability
• Improve type hinting and clarity

All existing pandas-related code, documentation, and tests should be removed accordingly.

Tasks:

• Identify and remove pandas-based classes, methods, and functions.
• Update type hints to reflect changes.
• Remove pandas-related unit tests.
• Update documentation and examples to exclusively use polars.

This will streamline future development efforts!

[Ben-geo]

@adamamer20
I was working on this issue and found [Bug]: agentsets_by_type won't work with duplicate types #124
I think once we discuss on how to solve that bug I can proceed
could you assign this issue to me as well.