[MINOR][SS][TEST] Use a managed temp dir for the checkpoint in KafkaRealTimeIntegrationSuite

[Kino1994]

What changes were proposed in this pull request?

Use a managed temp directory for the checkpointLocation of the e2e stateless test in KafkaRealTimeIntegrationSuite:

- .option("checkpointLocation", Files.createTempDirectory("some-prefix").toFile.getName)
+ .option("checkpointLocation", Utils.createTempDir().getCanonicalPath)

java.nio.file.Files was only used by that line, so its import is dropped.

Why are the changes needed?

Files.createTempDirectory(...) returns the full path of the directory it creates, but .toFile.getName keeps only the last segment of it:

full path   : /tmp/some-prefix7700179876677442263
getName()   : some-prefix7700179876677442263
isAbsolute  : false

So the option is a relative path, which Spark resolves against the working directory. Each run of the suite leaks two directories, neither of which is cleaned up:

• the temp directory that was created and then never used, under java.io.tmpdir
• the checkpoint itself, written into the module directory as connector/kafka-0-10-sql/some-prefix<N>

The second one is not covered by .gitignore, so it shows up as untracked in git status for anyone who runs the module's tests. After two full runs of sql-kafka-0-10 locally:

./connector/kafka-0-10-sql/some-prefix6311020086553351455
./connector/kafka-0-10-sql/some-prefix9434080927785378187
./target/tmp/some-prefix6311020086553351455
./target/tmp/some-prefix9434080927785378187

The suffixes pair up, one pair per run.

Utils.createTempDir() is what the rest of the module already uses for this: it is absolute, lives under java.io.tmpdir, and is deleted on JVM exit. The other five checkpointLocation usages in connector/kafka-0-10-sql all pass an absolute path from a managed temp directory; this line was the only one that did not.

Does this PR introduce any user-facing change?

No. Test-only.

How was this patch tested?

Ran KafkaRealTimeIntegrationSuite and confirmed the test still passes and that no some-prefix* directory is left behind afterwards, in the module directory or under target/tmp.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 5)

[uros-b]

LGTM, thank you @Kino1994!