Riemann zeta function

[jorenham]

This adds:

• zeta(s: f64) -> f64

[Copilot]

Pull Request Overview

This PR implements the Riemann zeta function by adding Rust bindings to the Boost Math library's zeta function implementation.

• Adds FFI binding for boost::math::zeta function
• Implements Rust wrapper with proper documentation and testing
• Integrates the new function into the module system

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
wrapper.cpp	Adds C++ wrapper function for boost::math::zeta
src/math/special_functions/zeta.rs	New module implementing the zeta function with documentation and tests
src/math/special_functions/mod.rs	Exports the new zeta module
src/math/mod.rs	Re-exports zeta function from special_functions
src/ffi.rs	Declares external C function for the zeta implementation

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