fix: Use the loaded Comet extension too (Spark 3.5.8)

[martin-g]

Which issue does this PR close?

Closes #.

Rationale for this change

In the diff for Spark 3.5.8 variable extensionClassNames is initialized with the items of extensionConfClassNames and loadCometExtension(sparkContext) but then it is not used.

The diff for 3.4.3 does use it:

datafusion-comet/dev/diffs/3.4.3.diff

Line 99 in 9b773f3

+ extensionClassNames.foreach { extensionConfClassName =>

What changes are included in this PR?

Iterate of the items of extensionClassNames.

How are these changes tested?

Run current test suite

[coderfender]

LGTM

[parthchandra]

nice catch @martin-g. There are CI failures though.

[martin-g]

Right!
The error is:

2026-03-18T09:55:23.5306977Z [info] - inject columnar AQE on *** FAILED *** (192 milliseconds)
2026-03-18T09:55:23.5309268Z [info]   java.lang.ClassCastException: class org.apache.spark.sql.catalyst.expressions.BoundReference cannot be cast to class org.apache.spark.sql.ColumnarExpression (org.apache.spark.sql.catalyst.expressions.BoundReference and org.apache.spark.sql.ColumnarExpression are in unnamed module of loader 'app')
2026-03-18T09:55:23.5312093Z [info]   at org.apache.spark.sql.BrokenColumnarAdd.withNewChildrenInternal(SparkSessionExtensionSuite.scala:927)
2026-03-18T09:55:23.5313407Z [info]   at org.apache.spark.sql.BrokenColumnarAdd.withNewChildrenInternal(SparkSessionExtensionSuite.scala:870)
...

[martin-g]

It seems to be a known problem: #1197

[martin-g]

Previously those tests were excluded for Comet - coderfender@24ee32e#diff-7917dac18d23e41523ceb1a298411e79bbf99d9349f885ac2c6c4ad81766265eR983-R984
Should I exclude them again or dive deeper and debug/fix them ?

Commit that removed the exclusion: andygrove@adcfce4

[parthchandra]

Previously those tests were excluded for Comet - coderfender@24ee32e#diff-7917dac18d23e41523ceb1a298411e79bbf99d9349f885ac2c6c4ad81766265eR983-R984 Should I exclude them again or dive deeper and debug/fix them ?

Commit that removed the exclusion: andygrove@adcfce4

We can exclude them for now.