Integrating sea ice into coupled data loaders

[William-gregory]

This is a first step towards integrating a stand-alone sea ice component into fme.coupled. This PR makes changes to:

• fme.coupled.data_loading
• fme.coupled.dataset_info
• fme.coupled.requirements

These changes both add a new ice component as well as make each atmosphere, ocean and ice component optional None. Therefore, if, for example, no atmosphere component is given, then the code assumes you are coupling an ocean model to an ice model. Similarly, if no ice component is given, then atmosphere-ocean coupling is assumed.

Had to make some additional changes outside of fme.coupled.data_loading to resolve some errors that pre-commit was throwing up around assertions. These include changes to fme.coupled.stepper, fme.coupled.aggregator, fme.coupled.inference.evaluator, fme.coupled.inference.test_evaluator, fme.coupled.inference.test_inference, fme.coupled.inference.loop, fme.coupled.inference.data_writer, fme.coupled.train, fme.coupled.test_stepper,