bindings for the remaining *_all legendre functions

[jorenham]

• legendre_p_all
• sph_legendre_p_all
• assoc_legendre_p_all
• lqmn

This also removes the out-of-scope-for-a-cpp-bindings-crate lqn alias.

[Copilot]

Pull Request Overview

This PR adds Rust bindings for the remaining *_all Legendre functions from the underlying mathematical library, completing the Legendre function bindings set. The changes enable computing arrays of Legendre polynomials at once rather than individually.

• Adds legendre_p_all, sph_legendre_p_all, assoc_legendre_p_all, and lqmn function bindings
• Refactors existing associated Legendre functions to use a unified interface with normalization parameter
• Removes the out-of-scope lqn alias (keeping the function itself)

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/lib.rs	Adds extern crate alloc and updates public exports to include new functions
src/legendre.rs	Implements all new *_all function bindings with Vec return types and comprehensive tests
src/bindings.rs	Adds helper functions for complex number handling and Vec conversions
build.rs	Adds C++ wrapper code for the new Legendre function bindings

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