Fix SSF issues on large grids

[vmitq]

Large molecules (e.g. ubiquitin) could fail during SSF grid reweighting step. Changing lddist type to size_t seems to fix it.

[Copilot]

Pull request overview

This PR widens the CUDA SSF distance-stride (lddist) from int32_t to size_t so the 1D SSF weight and derivative kernels can index the per-point distance scratch buffer without 32-bit overflow on large workloads. In the GauXC CUDA Scheme1 path, this change is aimed at the SSF reweighting logic used after grid-to-center distances are computed.

Changes:

• Update the CUDA SSF 1D kernel declarations/definitions to take size_t lddist.
• Propagate the widened stride type through the CUDA Scheme1 weight and first-derivative wrappers.
• Keep the CUDA Scheme1 call chain consistent with the existing size_t-based get_ldatoms() device stride.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/xc_integrator/local_work_driver/device/cuda/kernels/cuda_ssf_1d.hpp	Widened SSF 1D function declarations to use size_t for the distance stride.
src/xc_integrator/local_work_driver/device/cuda/kernels/cuda_ssf_1d.cu	Widened the SSF 1D kernel/function implementations for weight and derivative paths.
src/xc_integrator/local_work_driver/device/cuda/cuda_aos_scheme1_weights.hpp	Updated CUDA Scheme1 wrapper declarations to pass a size_t stride.
src/xc_integrator/local_work_driver/device/cuda/cuda_aos_scheme1_weights.cu	Propagated the widened stride through the CUDA Scheme1 wrapper implementations.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.