test: cover Iceberg driver commit cleanup

[sam-1112]

Which issue does this PR close?

Closes part of #5646 (driver-side Iceberg commit failure cleanup).

Rationale for this change

When every native write task succeeds but the driver-side Iceberg commit fails, Comet must abort the complete set of task commit messages. Otherwise, files produced by the failed write can be left behind as orphans.

What changes are included in this PR?

• Add a scoped, test-only pre-commit hook to IcebergCommitExec.
• Add a native Iceberg DELETE regression test that creates a real commit-time conflict after all task commit messages have been collected.
• Verify that the original Iceberg conflict reaches the caller, the concurrent append is the only committed change, and the failed DELETE’s files are removed from both storage and Iceberg metadata.
• Verify the failure path reaches both CometIcebergWriteExec and IcebergCommitExec.

How are these changes tested?

make core

./mvnw test -Pspark-3.5 -Dtest=none \
    '-Dsuites=org.apache.comet.CometIcebergWriteActionSuite driver commit failure aborts'

./mvnw test -Dtest=none \
    '-Dsuites=org.apache.comet.CometIcebergWriteActionSuite driver commit failure aborts'

./mvnw spotless:check -Pspark-3.5

Before merge, apply the run-iceberg-tests label to validate the Iceberg version matrix.