[SPARK-54629][CONNECT][TEST] Refactor fully-qualified class references to imports in SparkConnectJdbcDataTypeSuite

[xu20160924]

What changes were proposed in this pull request?

1. Refactor fully-qualified class references (e.g., java.sql.Date, java.util.Calendar, etc) to top-level imports to follow code style conventions
2. Add getString test coverage for BINARY type with UTF-8 encoding in "get binary type by column label" test

Why are the changes needed?

Test coverage

Does this PR introduce any user-facing change?

No

How was this patch tested?

./build/sbt -Phive "connect-client-jdbc/testOnly *SparkConnectJdbcDataTypeSuite" [info] Run completed in 26 seconds, 574 milliseconds. [info] Total number of tests run: 21 [info] Suites: completed 1, aborted 0 [info] Tests: succeeded 21, failed 0, canceled 0, ignored 0, pending 0 [info] All tests passed.

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

No

[xu20160924]

https://github.com/apache/spark/pull/53385#issuecomment-3627713243 I create new pull request based on the new commits.

[LuciferYang]

This is not mandatory; there are numerous similar cases in the current codebase.

[LuciferYang]

Merged into master. Thanks @xu20160924 and @pan3793