zeros of the kelvin functions

[jorenham]

• ber_zeros
• bei_zeros
• ker_zeros
• kei_zeros
• berp_zeros
• beip_zeros
• kerp_zeros
• keip_zeros
• kelvin_zeros

[Copilot]

Pull Request Overview

This PR adds support for computing zeros of Kelvin functions and their derivatives. It introduces 9 new public functions for finding the first nt zeros of individual Kelvin functions (ber, bei, ker, kei) and their derivatives (berp, beip, kerp, keip), plus a convenience function that returns zeros for all functions at once.

Key changes:

• Adds 8 individual zero-finding functions and 1 convenience function
• Modifies the kelvin function to return an array instead of a tuple for consistency
• Includes comprehensive test coverage with reference values from scipy

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/lib.rs	Exports the new Kelvin zero functions
src/kelvin.rs	Implements zero-finding functions and updates kelvin function signature
build.rs	Adds C++ wrapper for the klvnzo function

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}