[spark] Make DeletionVectorTest pass with write.use-v2-write enabled

[kerwin-zk]

Purpose

DeletionVectorTest fails when the suite is run with spark.paimon.write.use-v2-write=true.

Its helper runAndCheckSplitScan asserts that a DELETE/UPDATE/MERGE on a deletion-vector append table reads through a PaimonSplitScan (the V1 deletion-vector copy-on-write path). However, since #8539 added V2 delta-based row-level operations, an unaware-bucket deletion-vector append table with V2 write enabled is routed to PaimonSparkDeltaOperation / WriteDelta, whose scan side is a regular pushdown scan (see PaimonSparkDeltaOperation.newScanBuilder) and therefore produces no PaimonSplitScan. The assert(batchScans.nonEmpty) then fails:

- Paimon DeletionVector: delete for append non-partitioned table with bucket = -1 *** FAILED ***
  ArrayBuffer() was empty DELETE FROM T WHERE id = 2 (DeletionVectorTest.scala:85)

With the default (write.use-v2-write=false) the suite still exercises the V1 path, so the failure is only visible when V2 write is enabled. The delta path itself is functionally correct and covered by DeltaRowLevelOpsTest.

Tests

runAndCheckSplitScan now detects the V2 delta plan (WriteDelta, via EXPLAIN EXTENDED) and, in that case, just executes the statement instead of asserting the V1 split scan. Behavior is unchanged for the V1 path (default config and bucketed deletion-vector append tables), and the suite now passes under both write.use-v2-write=false and true.

API and Format

No public API or format change.

Documentation

No documentation change.

[Zouxxyy]

+1