Add examples/cpu_only.py based on code from PR feedback

https://github.com/NVIDIA/nvbench/pull/237#issuecomment-3058594793

python/examples/cpu_only.py

@@ -0,0 +1,18 @@
+import sys
+import time
+
+import cuda.nvbench as nvbench
+
+
+def throughput_bench(state: nvbench.State) -> None:
+    def launcher(launch: nvbench.Launch):
+        time.sleep(1)
+
+    state.exec(launcher)
+
+
+if __name__ == "__main__":
+    b = nvbench.register(throughput_bench)
+    b.setIsCPUOnly(True)
+
+    nvbench.run_all_benchmarks(sys.argv)