feat(PartitionedOutput): Add PrestoIterativePartitioningSerializer

This commit introduces PrestoIterativePartitioningSerializer, which
buffers RowVectors across multiple append() calls, partitions rows
in-place using PartitionedVector, and on flush() serializes each
non-empty partition into a Presto wire-format IOBuf. The serializer has
no dependency on velox_exec: it returns raw folly::IOBuf objects,
leaving SerializedPage creation to the caller.

Author: yingsu00

velox/serializers/CMakeLists.txt

@@ -29,6 +29,7 @@ velox_add_library(
   UnsafeRowSerializer.cpp
   PrestoBatchVectorSerializer.cpp
   PrestoHeader.cpp
+  PrestoIterativePartitioningSerializer.cpp
   PrestoIterativeVectorSerializer.cpp
   PrestoSerializerDeserializationUtils.cpp
   PrestoSerializerEstimationUtils.cpp