NREL Resstock and Comstock retrieval

[trevorb1]

Checklist

• I am using the current master branch
• I am running on an up-to-date pypsa-usa environment. Update via conda env update -f envs/environment.yaml

The Issue

For sector coupling studies, we use NREL comstock and resstock demand data. NREL recently did an update of this data and changed the format from *.csv to *.parquet. This causes the retrieval rules to break.

Steps To Reproduce

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Expected Behavior

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Error Message

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Anything else?

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