Fix an out of bounds access error

[rg20]

Description

This PR fixes an out of bound access introduced in #1140

Issue

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR fixes a dimension mismatch in the barrier solver's initial_point method. The nonnegative_variables mask is now constructed using data.x.size() instead of data.w.size(), ensuring dimensional consistency with the positivity enforcement operation that follows.

Changes

Dimension alignment in initial point

Layer / File(s)	Summary
nonnegative_variables mask dimension fix cpp/src/barrier/barrier.cu	Changed the nonnegative_variables vector construction from data.w.size() to data.x.size() to align mask dimensions with the subsequent data.x.ensure_positive(...) call when free variables are present.

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🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 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 directly matches the main change: fixing an out-of-bounds access error in the barrier solver.
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 identifies the issue (out of bounds access introduced in #1140) and explains the fix aligns mask dimensions with subsequent operations.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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[chris-maes]

LGTM. Thanks for the fix @rg20

[rg20]

/ok to test 107ef02

[rg20]

/ok to test 667a8a1

[rg20]

/merge