Add missing DataFrame methods (window, unnest_columns_with_options, drop_columns)

[timsaucer]

Summary

A few additional DataFrame methods from upstream DataFusion v53 are not yet exposed in datafusion-python.

Missing Methods

• window — apply window function expressions to the DataFrame
• unnest_columns_with_options — unnest array/struct columns with configurable options (e.g., recursion depth, preserve_nulls)
• drop_columns — drop columns by name (the existing drop method may not fully match upstream semantics)

Upstream Reference

• https://docs.rs/datafusion/53.0.0/datafusion/dataframe/struct.DataFrame.html

Implementation

• Rust bindings: crates/core/src/dataframe.rs
• Python wrappers: python/datafusion/dataframe.py

Note: This gap analysis was performed using an AI agent comparing upstream DataFusion v53 documentation against the current datafusion-python codebase.