Polars 2.0 makes streaming and disk spilling the default

Polars introduces version 2.0 that uses its streaming engine by default when collecting a LazyFrame, with spill-to-disk execution enabled for supported operations.

The release expands first-class SQL support with optimizer changes including join reordering and improved common-subplan elimination. It also introduces a native Map dtype and stricter dtype handling, including early schema validation through 'collect_schema()'.