Remove invalid CUDF_HOST_DEVICE annotations from constexpr variables

[bdice]

Description

CUDA 13.3 emits warning #1835-D when CUDF_HOST_DEVICE applies the function-only __host__ attribute to namespace-scope constexpr variables.

Remove the unnecessary annotation from all nine affected join and groupby constants. The constants remain usable in host and device constant expressions, preserving their values and behavior while avoiding the warning in cuDF and downstream CUDA builds.

Closes #24238.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 2ca9242 and 3db0ee3.

📒 Files selected for processing (3)

• cpp/src/groupby/hash/compute_shared_memory_aggs.cu
• cpp/src/groupby/hash/helpers.cuh
• cpp/src/join/key_remapping.cu

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📝 Summary

Summary by CodeRabbit

• Refactor
  • Streamlined internal compile-time configuration for join, grouping, and key-remapping operations.
  • Preserved existing values, calculations, and sentinel behavior while clarifying device-specific usage.
  • No user-visible functionality or behavior changes.

Walkthrough

The change removes unnecessary CUDF_HOST_DEVICE annotations from join and groupby compile-time constants. Constant values and computations remain unchanged. The groupby helper copyright notice is updated.

Changes

Compile-time constant annotation cleanup

Layer / File(s)	Summary
Update JoinNoMatch declaration cpp/include/cudf/join/join.hpp	Removed CUDF_HOST_DEVICE from JoinNoMatch while retaining its constexpr declaration and value.
Update join and groupby constants cpp/src/groupby/hash/compute_shared_memory_aggs.cu, cpp/src/groupby/hash/helpers.cuh, cpp/src/join/key_remapping.cu	Removed CUDF_HOST_DEVICE from internal constants and valid_extent. Their values and computations remain unchanged. Updated the copyright notice in helpers.cuh.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Change: Bug fix

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 3 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the primary change: removing invalid CUDF_HOST_DEVICE annotations from constexpr variables.
Description check	✅ Passed	The description directly explains the CUDA 13.3 warning, the removal of unnecessary annotations, the affected constants, and the preserved behavior. It is related to the changeset.

✨ Finishing Touches

🧪 Generate unit tests (beta)

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[PointKernel]

Holding this as the error repro doesn't seem legit to me.