[feat][spark-4.0.2] Avro data source changes (to_avro/from_avro, type widening, ZSTD pool, schema_of_avro) on GPU (cuDF)

[winningsix]

Background

Velox-native (cuDF) counterpart of the NVIDIA/spark-gluten issue for this Spark 4.0.2 feature. Depends on the native harness #66 and the JVM harness NVIDIA/spark-gluten#134.
Spark tickets:

• SPARK-47739
• SPARK-49082
• SPARK-46633
• SPARK-50350
• SPARK-46930
• SPARK-46746
• SPARK-46759
• SPARK-46766
• SPARK-43380
• SPARK-48545

Scope (native cuDF side)

• Implement / extend the cuDF GPU operators and expressions under velox/experimental/cudf/ backing this feature.
• Add / extend gtests under velox/experimental/cudf/tests/.
• Ensure CPU Velox tests are unaffected (VELOX_ENABLE_CUDF-gated).

Acceptance criteria — all pass on GPU (VELOX_ENABLE_CUDF=ON, ctest)

• StringFunctionTest (avro binary)
• CudfVectorTest

Cross-references

• Spark-Gluten (JVM) counterpart: NVIDIA/spark-gluten#153 (https://github.com/NVIDIA/spark-gluten/issues/153).
• Harness: [feat][spark-4.0.2] cuDF native test harness: build & run velox/experimental/cudf/tests on Spark-Flux GPU CI #66, NVIDIA/spark-gluten#134.

Notes

to_avro/from_avro as SQL functions; ZSTD buffer pool for Avro.