fix: transform function to support proper batch inference

[taepd]

Issue #, if available: This PR is related to #108 and #123.

Description of changes: As mentioned in #123, the batch inference provided by torchserve literally provides batch inference in a 'batch' format. However, the batch inference implementation in #108 simply runs a single inference through a loop. This is not a correct implementation of batch inference. TorchServe's documentation on batch inference, shows an example where the developer handles this logic and feeds the entire input batch to the model.

If I understand correctly, keeping the batch inference implementation in its current state would be deceptive to the user.

To make batch inference work correctly, we've modified it so that a list of requests can be sent to _transform_fn() in list format.

However, the current implementation requires modifications to related functions such as default_input_fn() and associated documentation, examples, etc. As far as I know, there is no better alternative, so it would be good to review and discuss this PR before proceeding with modifications to other functions.

Testing done: yes

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