fix[state win]: handle end all-null blocks error

[Tony2h]

Description

Please briefly describe the code changes in this pull request.

Jira: https://jira.taosdata.com:18080/browse/TD-38673

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @Tony2h, 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 resolves an issue in state window aggregation where blocks consisting entirely of null values were not handled correctly, leading to potential errors in window processing. The core change refines the logic for determining when to process or skip such blocks, ensuring that state windows are computed accurately even with null-heavy data. Comprehensive new test cases have been added to validate this fix across different state window extension scenarios.

Highlights

• State Window Null Block Handling: Modified the doStateWindowAggImpl function to correctly process state windows that contain blocks of all null values, especially when the extendOption is not set for backward extension. This addresses an issue where such blocks might have been incorrectly skipped.
• New Test Case for Null Blocks: Introduced a new test case, check_end_with_null_block, to validate the fix. This test populates a table with a large number of null rows followed by a single valid data point and then queries it using state_window with various extension options to ensure accurate results.
• Debug Logging: Added a temporary qInfo debug log in processClosedStateWindow to aid in debugging. This log should be removed before merging.

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[gemini-code-assist]

Code Review

This pull request addresses an issue with state window aggregation when a data block ends with all-null values. The fix in timewindowoperator.c correctly adjusts the logic to handle this case, especially for backward-extending state windows. The addition of new test cases in test_state_window_null_block.py is good, as it validates the fix for different state window extension options. My review identified one point of feedback: a leftover debug log statement that should be removed before merging.