New Parquet-Variant encoding

[AdamGS]

Summary

This PR introduces a new encoding to support Arrow's canonical extension type, but does not integrate it with anything else.

It does include basic pieces like slice/take/filter, and it can (or at least should) roundtrip with the equivalent arrow array.

Testing

The encoding includes a bunch of basic tests, both for making sure it roundtrips with arrow and for the various nullability cases.

[codspeed-hq]

Merging this PR will not alter performance

✅ 1106 untouched benchmarks
⏩ 1522 skipped benchmarks¹

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_{Comparing adamg/parquet-variant (338af8a) with develop (2383946)}

Footnotes

1. 1522 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[a10y]

It looks like this supports one typed_value per column. How would you represent something like this example, which shreds out multiple nested columns from an object?

Physically I think this differs from shredding out a struct column with two fields.

[AdamGS]

I think in that case it is a struct, because they are named

[AdamGS]

typed_value will be a struct (I think that's "object" in variant terms), but not directly of the event_type and event_ts types, but of ParquetVariant arrays that, but roughly:

Struct {
    "event_ts": Variant {
        ..,
        typed_value: Timestamp
    },
    "event_type": Variant {
        ..,
        typed_value: String
    },
}

[gatesn]

❤️

[AdamGS]

just moving things around