Update GauXC version

[awvwgk]

• include header guards for MPI and CUDA
• download json dependency if not available on system

[Copilot]

Pull Request Overview

This PR updates the GauXC version with improvements for better portability and dependency management. The changes add conditional compilation guards for CUDA and MPI functionality, and implement a fallback mechanism to download the nlohmann/json dependency when not available on the system.

Key changes:

• Added conditional compilation guards (#ifdef GAUXC_HAS_CUDA) around CUDA-specific includes to prevent compilation errors when CUDA is not available
• Updated MPI include from direct #include <mpi.h> to project-specific #include <gauxc/util/mpi.hpp> for better abstraction
• Implemented FetchContent-based fallback to download nlohmann/json v3.12.0 when the system version is not found

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
third_party/gauxc/src/xc_integrator/replicated/host/reference_replicated_xc_host_integrator_onedft.hpp	Adds conditional compilation for device runtime handling based on GAUXC_HAS_DEVICE
third_party/gauxc/src/xc_integrator/integrator_util/onedft_util.hpp	Guards CUDA-specific header inclusion with GAUXC_HAS_CUDA macro
third_party/gauxc/src/xc_integrator/integrator_util/onedft_util.cxx	Guards CUDA headers and updates MPI include to use project wrapper
third_party/gauxc/cmake/gauxc-onedft.cmake	Adds FetchContent logic to download nlohmann_json when not found on system
third_party/gauxc/cmake/gauxc-dep-versions.cmake	Defines repository and version for nlohmann_json dependency

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