EXAMPLES/DEVICE/EP: Added missing const to Buffer::query_mask_buffer.

[rakhmets]

What?

Added missing const to the declaration of Buffer::query_mask_buffer.
Added missing const to a parameter of ep_kernels::query_mask_buffer.

Why?

To improve the readability of the code, following C++ core guidelines.
Spotted by the PR (#1793), need to reduce the size of the PR, removing unrelated changes.

[coderabbitai]

📝 Walkthrough

Walkthrough

query_mask_buffer now treats the input mask as read-only across the CUDA and Buffer interfaces. The Buffer method is const-qualified and uses a typed tensor data accessor while retaining existing validation.

Changes

Query mask buffer const correctness

Layer / File(s)	Summary
CUDA query interface constness examples/device/ep/csrc/kernels/api.cuh, examples/device/ep/csrc/kernels/nixl_ep_ll.cu	Kernel and host wrapper signatures now accept mask_buffer_ptr as const int*.
Buffer query implementation constness examples/device/ep/csrc/nixl_ep.hpp, examples/device/ep/csrc/nixl_ep.cpp	Buffer::query_mask_buffer is const-qualified and passes the validated tensor through data_ptr<int>() while preserving existing checks.

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

Suggested reviewers: ebarilanM

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title is concise and accurately summarizes the main change: adding missing const qualifiers to Buffer::query_mask_buffer.
Description check	✅ Passed	The description covers What and Why clearly, and the optional How section is acceptable to omit for this small change.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[rakhmets]

/build