[Release-2.67] Cherry pick #35743 into release branch

[Abacn]

• Fix BeamSQL CalcRel DATETIME expression

• Add nullable array test case

• fix checkstyle

Please add a meaningful description for your change here

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[gemini-code-assist]

Summary of Changes

Hello @Abacn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request cherry-picks a fix for BeamSQL's CalcRel DATETIME expression handling and introduces a new test case for nullable arrays. My primary goal is to ensure correct processing of various Joda-Time instant types within SQL queries and to improve test coverage for complex data types.

Highlights

• BeamSQL DATETIME Expression Fix: I've updated the BeamCalcRel to correctly handle DATETIME expressions by casting values to AbstractInstant instead of DateTime. This change ensures compatibility with both Instant and DateTime objects from Joda-Time when retrieving milliseconds.
• New Nullable Array Test Case: I've added a new test method, testNestedDatetime, in BeamComplexTypeTest to validate the behavior of nested arrays containing DATETIME values, specifically including cases with null elements. This enhances the robustness of BeamSQL's type handling.

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