RecordReader Permits Illegal Types

[tustvold]

Describe the bug

Originally pointed out by @jorgecarleitao here.

It is currently possible to construct RecordReader<T> and by extension PrimitiveArrayReader with any T: DataType. This is despite an explicit assumption in RecordReader's buffering logic that DataType::T can be zero-initialized and stored in MutableBuffer.

Fortunately DataType::T: ParquetValueType which is a sealed trait, however, ParquetValueType is implemented for types such as Int96 and ByteArray which aren't POD.

To Reproduce

PrimitiveArrayReader::<ByteArrayType>::new(...)

Expected behavior

It shouldn't be possible to construct PrimitiveArrayReader with invalid types