Stirling numbers of the 2nd kind

[jorenham]

closes #128

[Copilot]

Pull Request Overview

This PR implements Stirling numbers of the second kind as a new function stirling2 in the xsf-rust library. The implementation provides a pure Rust translation of scipy.special.stirling2(n, k, exact=True).

Key changes:

• Adds stirling2<T> function with dynamic programming implementation and special case optimizations
• Includes comprehensive documentation with mathematical notation and cross-references
• Provides test coverage using precomputed values in a lookup table

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/scipy_special/stirling.rs	New module implementing stirling2 function with dynamic programming algorithm, special case handling, and test suite
src/scipy_special/mod.rs	Module declaration and public re-export of stirling functions
src/lib.rs	Updated combinatorics documentation table to include stirling2 instead of planned placeholder

[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.