Use ms for number report (#5362)

Summary:
ns * 1e-6 = ms

Example output:
(9.36ms inference mv2_xnnpack)
```
[{"actualValue":9.3611927,"benchmarkModel":{"backend":"","name":"mv2_xnnpack","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"avg_inference_latency(ms)","targetValue":0.0},{"actualValue":27.418698,"benchmarkModel":{"backend":"","name":"mv2_xnnpack","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"model_load_time(ms)","targetValue":0.0},{"actualValue":0.0,"benchmarkModel":{"backend":"","name":"mv2_xnnpack","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"load_status","targetValue":0.0}]
```

and for LLM
(12.34 tps mocked number)
```
[{"actualValue":0.0,"benchmarkModel":{"backend":"","name":"et_exported_llama","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"load_status","targetValue":0.0},{"actualValue":3375.450312,"benchmarkModel":{"backend":"","name":"et_exported_llama","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"model_load_time(ms)","targetValue":0.0},{"actualValue":8220.467966,"benchmarkModel":{"backend":"","name":"et_exported_llama","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"generate_time(ms)","targetValue":0.0},{"actualValue":12.3456,"benchmarkModel":{"backend":"","name":"et_exported_llama","quantization":""},"deviceInfo":{"arch":"SM-S926U1","availMem":0,"device":"samsung","os":"Android 14","totalMem":0},"metric":"token_per_sec","targetValue":0.0}]
```

Pull Request resolved: https://github.com/pytorch/executorch/pull/5362

Reviewed By: huydhn

Differential Revision: D62665456

Pulled By: kirklandsign

fbshipit-source-id: 3d2444d90aef82bd5f331838a89319be9e9797e5