Parquet: Support repetition level >1 and multi-column fields

[rcaudy]

Currently, we regard nested repetition and multi-column fields as uncommon and hard to map into a columnar data table like Deephaven's.
This feature request is intended to capture views to the contrary.

Linked to #294 , although intended for a later effort.

[rcaudy]

Likely the first step is some kind of "flattening", but this is contrary to the intent of the Dremel design, so maybe we can think of a better solution.

[rcaudy]

I'll be improving our error messages with a PR shortly. New messages:
For:

t = io.deephaven.db.tables.utils.ParquetTools.readTable("/data/parquetFiles/nonnullable_nested_v1_IMPALA_NULLS_NONE.parquet")

We'll see:

java.lang.UnsupportedOperationException: Unsupported maximum repetition level 2 in column int_array_array/list/element/list/element

For:

t = io.deephaven.db.tables.utils.ParquetTools.readTable("/data/parquetFiles/repeated_nested_RUST_NONE.parquet")

We'll see:

java.lang.UnsupportedOperationException: Encountered unsupported multi-column field phoneNumbers: found columns phoneNumbers/phone/number and phoneNumbers/phone/kind

[devinrsmith]

It might be nice to be able to specify which columns you care about for your Table - in which case, the user can choose to not include the nested columns.

There's a mechanism right now to provide column instructions:

from deephaven.parquet import read, ColumnInstruction

t = read(
    path="/snappy.parquet",
    col_instructions=[
        ColumnInstruction(column_name="date", parquet_column_name="date")
    ],
)

but this currently throws the error:

java.lang.UnsupportedOperationException: Encountered unsupported multi-column field outputs: found columns outputs/list/element/address and outputs/list/element/index
	at io.deephaven.parquet.table.ParquetSchemaReader.lambda$readParquetSchema$1(ParquetSchemaReader.java:174)
	at java.base/java.util.HashMap.compute(HashMap.java:1316)
	at io.deephaven.parquet.table.ParquetSchemaReader.readParquetSchema(ParquetSchemaReader.java:169)
	at io.deephaven.parquet.table.ParquetTools.convertSchema(ParquetTools.java:647)
	at io.deephaven.parquet.table.ParquetTools.readTableInternal(ParquetTools.java:384)
	at io.deephaven.parquet.table.ParquetTools.readTable(ParquetTools.java:94)

[devinrsmith]

A user has hit this w/ the parquet viewer, see devinrsmith/deephaven-parquet-viewer#9