[Spark] SparkWidthBucket return_type is Int32, should be Int64 to match Spark

[mbutrovich]

Describe the bug

SparkWidthBucket::return_type returns Int32, but Spark's WidthBucket.dataType is LongType:

https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala#L1825

// datafusion/spark/src/function/math/width_bucket.rs
fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
    Ok(Int32)
}

The n_bucket input was aligned to i64 to match Spark in #20330, but the return type was left as Int32. The kernel still builds Int32Array.

This produces wrong results in any consumer that plans against Spark's declared output type (Int64) but receives an Int32Array at runtime: with two rows per batch, the consumer reads 16 bytes of Int64 from an 8-byte Int32 buffer, packing two int32 values into a single int64 and reading uninitialized bytes for the rest.

Concretely, for width_bucket(value, 0.0, 10.0, 5) over Range(0, 10) split into 5 partitions of 2 rows each:

value	expected (Int64)	observed
0	1	4294967297 (= 0x1_00000001)
1	1	0
2	2	8589934594 (= 0x2_00000002)
3	2	0
...	...	...

To Reproduce

Run any consumer that respects Spark's declared LongType for WidthBucket against SparkWidthBucket. Reproduces in DataFusion Comet on the width_bucket - with range data test in CometMathExpressionSuite (apache/datafusion-comet#4347).

Expected behavior

SparkWidthBucket::return_type returns Int64 and the kernel builds Int64Array, matching Spark.

Additional context

Related: #20330 (input parameter alignment).

[mbutrovich]

Debating whether this is a Comet issue or not, hence the opening and closing. We can work around it in Comet, but this might still be worth addressing here in DataFusion.

[mbutrovich]

Ideally I think these expressions should produce the expected types for Spark. I'm having to write workaround code in Comet when they don't align, and really we should just respsec the Spark type here.