Array functions fall back to Spark for binary and struct element types (`ArraysBase` type gate)

[andygrove]

Part of #5572.

ArraysBase.isTypeSupported (spark/src/main/scala/org/apache/comet/serde/arrays.scala:888) rejects BinaryType outright and StructType pending #1307, and childTypesSupportLevel turns that into Unsupported:

.map(dt => Unsupported(Some(s"data type not supported: $dt")))

arrays.scala:911

Seven serdes mix in ArraysBase: CometArrayRemove (:36), CometFlatten (:700), CometArrayPosition (:791), CometShuffle (serde/collectionOperations.scala:64), CometArrayInsert (:409), CometCreateArray (:503) and CometArrayReverse (:572). None routes the declined types through the dispatcher, so array<struct<...>> and array<binary> — both very ordinary shapes in nested Parquet data — fail the whole projection back to Spark.

docs/source/user-guide/latest/expressions.md already records this for three of them: array_position, flatten and shuffle all carry "Binary/struct/map elements fall back".

Both element types are admitted by CometBatchKernelCodegen.isSupportedDataType, which handles ArrayType, StructType and MapType recursively and accepts BinaryType as a leaf.

One important carve-out: the "null elements" half of those doc notes is not dispatchable. NullType is absent from isSupportedDataType, so array<null> will still fall back and the doc notes should be updated to say so rather than being deleted wholesale.

CometShuffle is nondeterministic, which is fine — canHandle explicitly admits nondeterministic and stateful expressions, and each cache entry gets a single init(partitionIndex) call. Worth a test that confirms the shuffled permutation still matches Spark through the dispatcher.

CometArrayInsert, CometCreateArray and CometArrayReverse also decline inside convert, which the dispatcher cannot see; see the prerequisite issue on convert-side declines.