MVP: Wrapping read_parquet

[dougbrn]

Feature request
Blocks #9. Implement a wrapper for read_parquet that provides a more tailored interface for loading a "base" (main) parquet file and a set of additional parquet files that are automatically packed into nested columns in the base parquet file. E.g.

read_parquet(data="base.parquet", to_pack={"dia": "nested.parquet"})

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