Avoid tracking counter underflow

[bdice]

Description

Prevents tracking_resource_adaptor from decrementing allocated_bytes_ for untracked deallocations. The counter is now reduced only when a pointer is found and erased from the tracked allocation map.

I verified that TrackingTest.UntrackedDeallocationDoesNotUnderflowAllocatedBytes fails without the fix.

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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[coderabbitai]

📝 Walkthrough

Walkthrough

The PR fixes an underflow bug in tracking_resource_adaptor by moving the allocated_bytes_ decrement operation inside the nonzero-bytes guard in the deallocate method. A new test validates that untracked deallocations through nested adaptors do not underflow accounting.

Changes

Untracked deallocation fix

Layer / File(s)	Summary
Untracked deallocation accounting fix cpp/src/mr/detail/tracking_resource_adaptor_impl.cpp, cpp/tests/mr/tracking_mr_tests.cpp	deallocate moves allocated_bytes_ -= bytes inside the if (bytes != 0) block after removing the allocation record, preventing underflow when deallocations occur through a different tracking adaptor. Test validates both adaptors report zero allocations after outer allocation and inner deallocation of the same pointer.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• rapidsai/rmm#2316: Adjusts tracking_resource_adaptor deallocation accounting to prevent incorrect allocated_bytes_ updates in zero/untracked deallocation edge cases.
• rapidsai/rmm#2304: Modifies tracking_resource_adaptor_impl deallocate logic and extends tracking_mr_tests.cpp to cover deallocation correctness scenarios.

Suggested reviewers

• ttnghia
• PointKernel
• harrism

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing counter underflow in the tracking resource adaptor, which is exactly what the changeset addresses.
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.
Description check	✅ Passed	The pull request description clearly explains the fix: preventing allocated_bytes_ from being decremented for untracked deallocations, with specific details about when the counter is reduced.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[bdice]

/merge