feat: Implement <expr>$arr$agg() and <expr>$list$agg()

[etiennebacher]

Part of #1397

[Copilot]

Pull Request Overview

This PR implements <expr>$arr$agg() and <expr>$list$agg() methods, which run aggregation expressions against array/list elements and automatically explode the result when the expression returns a scalar. This is similar to the existing $eval() methods but with automatic scalar handling.

Key Changes:

• Added Rust implementations for arr_agg() and list_agg() that wrap the underlying Polars methods
• Added R wrapper functions with comprehensive documentation and examples
• Added tests covering both scalar and non-scalar return value scenarios

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/rust/src/expr/list.rs	Implements list_agg() method calling Polars' native list().agg()
src/rust/src/expr/array.rs	Implements arr_agg() method calling Polars' native arr().agg()
R/expr-list.R	Adds expr_list_agg() function with documentation and examples
R/expr-array.R	Adds expr_arr_agg() function with documentation and examples (contains documentation issues)
tests/testthat/test-expr-list.R	Tests for list$agg() covering scalar and non-scalar returns
tests/testthat/test-expr-array.R	Tests for arr$agg() covering scalar and non-scalar returns
R/000-wrappers.R	Auto-generated FFI wrappers for the new methods
src/init.c	Auto-generated C bindings registration
src/rust/api.h	Auto-generated FFI declarations
man/expr_list_agg.Rd	Generated documentation for list aggregation (contains minor dtype issue)
man/expr_arr_agg.Rd	Generated documentation for array aggregation (contains documentation issues)
altdoc/mkdocs.yml	Updated navigation to include new documentation pages
NEWS.md	Added changelog entry for the new feature

[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

[eitsupi]

Thanks!