Use of LazyFrames for Polars implementation

Polars has a lazy API, which allows for query optimization. Currently, AgentSetPolars and PolarsMixins are implemented with the eager API, which may lead to a significant performance loss. Collection could be done at each step.

References:
- https://docs.pola.rs/user-guide/concepts/lazy-vs-eager/
- https://stackoverflow.com/questions/76612163/what-are-the-advantages-of-a-polars-lazyframe-over-a-dataframe

Start with AgentSetPolars and PolarsMixins, then read the linked Polars lazy-versus-eager API reference to understand the intended query optimization. Compare the current eager operations with the proposed lazy workflow and review pull request #144 before starting. Done means the implementation uses LazyFrames where appropriate without changing its existing behavior.

Written by the indexing model from the issue text.