Remove torch/motmetrics/pandas requirements and skip related tests

[holger-motional]

This PR removes the tracking and prediction requirements from the default nuscenes-devkit installation. They can still be installed manually. The major implication of this is that all unit test which require these packages would fail. We therefore catch ModuleNotFoundErrors when importing the modules torch, motmetrics and pandas.

Here is the test output without those requirements installed:

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Ran 179 tests in 21.658s

Here is the test output with those requirements installed:

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Ran 203 tests in 36.815s

OK

[whyekit-motional]

Looks good!