feat: expose PyWindowFrame

[dlovell]

Which issue does this PR close?

Partial progress on #191 : Expressions: Window function

What changes are included in this PR?

This PR

• adds PyWindowFrame
• modifies functions.window to accept an optional PyWindowFrame and optional PySessionContext
  • PySessionContext is necessary to look up aggregates registered via PySessionContext.register_udaf
• modifies function.window to fall back to SessionContext.udaf when find_df_window_func fails
• modifies Accumulator impl for RustAccumulator to expose retract_batch and supports_retract_batch

Are there any user-facing changes?

PyWindowFrame needs to be documented as do changes to functions.window

note: I have working code that enables window functions for ibis that I still need to create a PR for

[andygrove]

Build is failing due to new clippy rule in latest Rust. I have a fix in https://github.com/apache/arrow-datafusion-python/pull/511

[andygrove]

@dlovell Could you upmerge to pick up the clippy fix?

[dlovell]

@andygrove i hadn't heard the term upmerge before, but i presume that means merge main into pywindowframe. let me know if i should do something else.

[andygrove]

@andygrove i hadn't heard the term upmerge before, but i presume that means merge main into pywindowframe. let me know if i should do something else.

Yes, exactly.