Pre-Release of Polars 2.0

Polars 2.0 is releasing its first release candidate with the primary goal of cleaning up legacy design decisions and changing defaults rather than adding major new features. The biggest change is making the streaming engine the default for LazyFrame queries, which is expected to deliver 5x faster performance and significantly lower memory usage for most users, though it no longer guarantees row order for certain operations like joins and group_by unless explicitly requested. The release also emphasizes stricter error handling to catch issues earlier in data pipelines and provide faster feedback for AI-driven development.