Add memory resource parameter to cudf::key_remapping constructor

[PointKernel]

Description

Follow-up to #23264.

This PR adds an mr parameter to the cudf::key_remapping constructor to control the memory usage of the internal cuco hash table, to better align with the temporary mr effort (#20780).

Checklist

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

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[PointKernel]

/ok to test 85a48e3

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 617b764 and b4db21e.

📒 Files selected for processing (1)

• cpp/tests/join/key_remapping_tests.cpp

🚧 Files skipped from review as they are similar to previous changes (1)

• cpp/tests/join/key_remapping_tests.cpp

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📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added support for selecting a custom device memory resource when creating key remapping operations.
  • Existing behavior remains unchanged when no memory resource is specified.

• Tests

  • Added coverage validating custom memory resource usage and preserving expected key-matching results.

Walkthrough

The key_remapping constructor now accepts an optional device memory resource, propagates it to the internal CUCO hash table, and includes a test verifying allocation metrics and remapping behavior with an explicit resource.

Changes

Key remapping memory resource

Layer / File(s)	Summary
Memory resource contract and allocator propagation cpp/include/cudf/join/key_remapping.hpp, cpp/src/join/key_remapping.cu	Adds the optional memory resource parameter and forwards it through key remapping construction into the CUCO allocator.
Explicit resource validation cpp/tests/join/key_remapping_tests.cpp	Adds a statistics-resource test that checks peak allocation usage and duplicate/distinct key remapping results.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: wence-, lamarrr

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: adding a memory resource parameter to the key_remapping constructor.
Description check	✅ Passed	The description is directly related to the changeset and accurately describes the new mr parameter and its purpose.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@cpp/tests/join/key_remapping_tests.cpp`:
- Around line 761-766: In the remap_right_keys test, add an assertion that ids
contains the expected number of rows before the indexed EXPECT_EQ and EXPECT_NE
checks. Keep the existing ID relationship assertions unchanged and ensure all
ids[0] through ids[3] accesses occur only after validating the output length.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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Configuration used: Path: .coderabbit.yaml

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📥 Commits

Reviewing files that changed from the base of the PR and between 9d9fec8 and 617b764.

📒 Files selected for processing (3)

• cpp/include/cudf/join/key_remapping.hpp
• cpp/src/join/key_remapping.cu
• cpp/tests/join/key_remapping_tests.cpp

[vyasr]

@PointKernel needs a style fix.

[PointKernel]

/merge