add oneflow.clone api

[marigoold]

close #9795

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Speed stats:

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Speed stats:

GPU Name: GeForce GTX 1080 









❌ OneFlow resnet50 time: 139.9ms (= 13988.2ms / 100, input_shape=[16, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 160.8ms (= 16081.2ms / 100, input_shape=[16, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.15 (= 160.8ms / 139.9ms)

OneFlow resnet50 time: 85.0ms (= 8504.0ms / 100, input_shape=[8, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 102.8ms (= 10277.2ms / 100, input_shape=[8, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.21 (= 102.8ms / 85.0ms)

OneFlow resnet50 time: 58.0ms (= 11605.0ms / 200, input_shape=[4, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 88.6ms (= 17715.2ms / 200, input_shape=[4, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.53 (= 88.6ms / 58.0ms)

OneFlow resnet50 time: 45.7ms (= 9145.8ms / 200, input_shape=[2, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 77.1ms (= 15426.0ms / 200, input_shape=[2, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.69 (= 77.1ms / 45.7ms)

OneFlow resnet50 time: 40.8ms (= 8157.3ms / 200, input_shape=[1, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 73.3ms (= 14650.2ms / 200, input_shape=[1, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.80 (= 73.3ms / 40.8ms)

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View latest API docs preview at: https://staging.oneflow.info/docs/Oneflow-Inc/oneflow/pr/9800/