Move and update process_parquet from presto-worldcereal

[kvantricht]

Copied from WorldCereal/presto-worldcereal#124:

• no longer infer frequencies from the data but accept them as input
• for now only implement two options: "month", "dekad"
• Look for the occurrence of missing timestamps and if needed fill them with nodata (log a warning for user). Actual timestamps should be constructed with convenience functions for date ranges (e.g. dekad not supported natively by pandas)
• Move process_parquet in its entirety to worldcereal-classification repo: https://github.com/WorldCereal/worldcereal-classification/blob/main/src/worldcereal/utils/refdata.py