Add support of PyTorch and Jax to EfficentNetV1, EfficientNetLite, and RegNet Model

[cosmo3769]

Since the three models is almost completely converted to backbone.

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I am willing to add support of Pytorch and JAX to these models as well. Should I add it in these created PR only or should I create another PR for this?

@ianstenbit @jbischof @LukeWood

[ianstenbit]

Let's do it in the open PR that you have -- let me know if you have any trouble converting the backbones.

Here's an example PR you can use to see how to add Keras Core support: https://github.com/ianstenbit/keras-cv/pull/4/files