Fix Dask KMeans performance regression

[viclafargue]

Closes #7749

The KMeans parameter struct on cuML side used to be calloc'ed, and is now constructed on stack. Because of this, Dask Kmeans used to use raft::random::GeneratorType::GenPhilox (value of 0) as its random number generator type and now uses raft::random::GeneratorType::GenPC (constructor default of 1). This somehow causes the KMeans initialization or convergence steps to be of lower quality. Converges in ~40 steps instead of 2.

This PR fixes the issue by setting raft::random::GeneratorType::GenPhilox as the default inside of the cuML parameter struct default values.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Updated copyright year information in cluster module

Walkthrough

The change updates the default RNG state initialization in KMeansParams to explicitly specify the GenPhilox generator type in addition to the seed value. The copyright year header is also incremented from 2025 to 2026.

Changes

Cohort / File(s)	Summary
KMeansParams RNG initialization cpp/include/cuml/cluster/kmeans_params.hpp	Updated rng_state default initialization from {0} to {0, raft::random::GeneratorType::GenPhilox} to explicitly specify the generator type. Copyright year updated from 2025 to 2026.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly describes the main change: fixing a Dask KMeans performance regression, which is the primary objective of this PR.
Description check	✅ Passed	The description clearly explains the regression cause, technical details of the fix, and references the linked issue #7749.
Linked Issues check	✅ Passed	The PR fixes the performance regression by restoring the original RNG generator type (GenPhilox) as default, directly addressing the root cause identified in issue #7749.
Out of Scope Changes check	✅ Passed	All changes are limited to the KMeansParams header file RNG initialization and copyright update, directly related to fixing the reported issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[viclafargue]

/merge