Comet should fallback to Spark for unsupported partitioning

[viirya]

Describe the bug

Found this bug during fixing Spark SQL test failure in org.apache.spark.sql.connector.KeyGroupedPartitioningSuite for #651.

[info] - SPARK-44647: shuffle one side and join keys are less than partition keys *** FAILED *** (24 milliseconds)                                                                                                                     
[info]   java.lang.IllegalStateException: Exchange not implemented for KeyGroupedPartitioning(List(item_id#9849L),3,List([1], [3], [4]),List())

Steps to reproduce

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Expected behavior

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Additional context

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