Update positional encodings in model to be purely local #1109

Describe the task. It can be a feature, documentation, etc.

Currently, various positional encodings assuming a fixed healpix grid and use absolute coordinates. This should be changed to relative positional encodings to avoid grid artifacts--if possible and the skill is not degraded by this.

Hedgedoc URL, if you are keeping notes, plots, logs in hedgedoc.

No response

Area

• datasets, data readers, data preparation and transfer
• model
• science
• infrastructure and engineering
• evaluation, export and visualization
• documentation