nixos/slurm: expose NVML library when NVIDIA datacenter is enabled

When `hardware.nvidia.datacenter.enable` is turned on we likely want the
NVIDIA Management Library (NVML) at runtime so that Slurm can query GPU
metrics. This adds the driver directory containing `libnvidia‑ml.so` to
`slurmd` environment's `LD_LIBRARY_PATH`, making it discoverable.

nixos/modules/services/computing/slurm/slurm.nix

@@ -453,6 +453,8 @@ in
         users.groups.slurmrestd = lib.mkIf (cfg.rest.enable) { };
 
         systemd.services.slurmd = lib.mkIf (cfg.client.enable) {
+
+          environment.LD_LIBRARY_PATH = lib.mkIf config.hardware.nvidia.datacenter.enable "/run/opengl-driver/lib";
           path =
             with pkgs;
             [