fix: preserve GROUPING SET dimensions with single-value filter

[Shekharrajak]

Fixes #13204

Description

SELECT dim1, dim2, SUM(cnt)
FROM druid.foo
WHERE dim2 = 'a'
GROUP BY GROUPING SETS ( (dim1, dim2), (dim1) )

Before (incorrect):

dim1 | dim2 | SUM(cnt)
""   | a    | 1
"1"  | a    | 1
""   | a    | 1   -- should be null
"1"  | a    | 1   -- should be null

After (correct):

dim1 | dim2 | SUM(cnt)
""   | a    | 1
"1"  | a    | 1
""   | null | 1
"1"  | null | 1

Fixed Grouping.applyProject() to preserve non-literal dimensions (and literal dimensions referenced in non-empty
subtotals) when Subtotals.hasEffect() is true, preventing single-value filter dimensions from being dropped and
causing incorrect non-null values in GROUPING SET subtotal rows.

Release note

Fixed a bug where a SQL query using GROUPING SETS with a single-value WHERE filter on a grouped dimension would return
the filtered value instead of null in subtotal rows that exclude that dimension. For example, WHERE dim2 = 'a' GROUP
BY GROUPING SETS ((dim1, dim2), (dim1)) now correctly returns null for dim2 in the (dim1) subtotal rows instead of
repeating 'a'.

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This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[FrankChen021]

The changes LGTM, no correctness issues found.

[FrankChen021]

I have reviewed the code for correctness, edge cases, concurrency, and integration risks; no issues found.

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This is an automated review by Codex GPT-5

[Shekharrajak]

Thanks @FrankChen021 for review. @a2l007 can you please have a look and lets merge it.

[Shekharrajak]

@jtuglu1 Please have a look.

[jtuglu1]

Can we add some quidem tests?

[FrankChen021]

I have reviewed the updated code for correctness, edge cases, concurrency, lifecycle, and integration risks; no issues found.

Reviewed 3 of 3 changed files.

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This is an automated review by Codex GPT-5.5