[shardformer] adapted T5 and LLaMa test to use kit

[FrankLeeeee]

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Fixed #4044
Fixed #4037

This PR is a continuation of #4045 and #4036

📝 What does this PR do?

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This PR adapted the T5 and LLaMA tests to use the tests/kit/model_zoo. The changes can be summarized as:

1. added a loss_fn in the model_zoo to compute a dummy loss from the model output
2. extracted the common functions for test_model
3. integrated model_zoo to test_model

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