Demonstrate corrdiff inference from earth2

nvidia earth2 offers a pretrained downscaling model (CMIP6 to ERA5), which could be used for demonstrating at the hackathon.

- [ ] set up environment on JASMIN
- [ ] download sample data
- [ ] create pet accessor
- [ ] create tutorial notebook for running model
- [ ] create PET pipeline
- [ ] visualise data
- [ ] calculate scores

Start by reviewing the earth2 downscaling model and the checklist in this issue, then determine the JASMIN environment and sample data needed. The work involves a pet accessor, tutorial notebook, PET pipeline, visualisation and score calculation; it is done when each listed demonstration step is completed.

Written by the indexing model from the issue text.