Function dictionary_page_crypto_context 

fn dictionary_page_crypto_context(
    parquet_meta_data: &ParquetMetaData,
    column_metadata: &ColumnChunkMetaData,
    row_group_idx: usize,
    column_idx: usize,
) -> Result<Option<Arc<CryptoContext>>>

Builds the crypto context needed to decrypt the dictionary page of column_metadata, or None if the file (or this column) isn’t encrypted.