Change the is_weights_f32 CUDA kernel signature from taking total_sum as
a scalar f32 argument (which requires a CPU readback) to reading it from
a const float* GPU-resident pointer. This eliminates the last memcpy_dtoh
in the PER sampling hot path.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>