test: seed MSQ quantiles sketch for partition tests

[gitedmond]

Fixes #20439.

Description

ClusterByStatisticsCollectorImplTest fixes the input shuffle order, but the DataSketches ItemsSketch also uses a shared random generator when it compacts and merges. Different sketch samples can push a partition outside the test's fixed weight leeway.

Seed the sketch generator before each test method so the existing partition coverage, boundary, and weight assertions run against a repeatable sample. This changes only the test; production partitioning is unchanged. Seed 0L reproduced the same weight failure for this fixture, so the test uses 1L after checking the target method and the full class.

Verification

• Before the change, with Surefire retries disabled, the target method failed on the second unseeded run: single collector, random order, generatePartitionsWithMaxCount(50), partition #13, at verifyPartitionWeights.
• After the change, all 15 tests in ClusterByStatisticsCollectorImplTest passed with retries disabled.
• The formerly flaky method passed five additional isolated runs with retries disabled.
• git diff --check passed.

Tests used JDK 25 and Maven 3.9.16 with -pl multi-stage-query -am, -Pskip-static-checks, and -Dweb.console.skip=true.

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Key changed/added classes in this PR

• ClusterByStatisticsCollectorImplTest

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This PR has:

• been self-reviewed.

[FrankChen021]

🟢 Approval recommended

No actionable issues found. The change is limited to the test class and uses DataSketches' documented deterministic-test random hook; resetting it before each test makes each method repeatable without changing production behavior. I inspected the full changed class, the collector and sketch call paths, the pinned DataSketches 4.2.0 source/API, module test execution settings, related MSQ tests, and the existing ItemsSketch test pattern.

Reviewed 1 of 1 changed files.

Validation: Static review completed; git diff --check passed. No build or test commands were run.

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This is an automated review by Codex GPT-5.6-Luna(max)