Fix erroneous early solve termination

[aliceb-nv]

#2003 introduced an early termination checking path when solutions arrive to the B&B by checking against the dual bound.
However, for early heuristics that run before B&B begins its solve, the dual bound may in some cases be uninitialized, which can cause early termination even though the gap is still large.

This PR introduces a fix by initializing the numerical lower bound to inf before B&B solve starts.

Description

Issue

Checklist

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• Testing
  • New or existing tests cover these changes
  • Added tests
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• Documentation
  • The documentation is up to date with these changes
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[aliceb-nv]

/ok to test 263179d

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• cpp/src/branch_and_bound/branch_and_bound.hpp

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📝 Walkthrough

Walkthrough

The branch-and-bound numerical lower bound now starts at positive infinity instead of an unspecified value.

Changes

Branch-and-bound initialization

Layer / File(s)	Summary
Set the initial numerical lower bound cpp/src/branch_and_bound/branch_and_bound.hpp	lower_bound_numerical_ now initializes to positive infinity.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Bug fix

Suggested reviewers: nguidotti

Merge Risk: ⚪ Minimal · up to 26317

The initialization does not create a premature-solve path; bound consumers handle the infinity sentinel. No actionable merge-blocking issue remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: preventing erroneous early solve termination caused by an uninitialized bound.
Description check	✅ Passed	The description directly explains the uninitialized numerical lower bound and the fix implemented in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 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.

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[Bubullzz]

great catch !

[github-actions]

CI Test Summary

✅ All 32 test job(s) passed.

[nguidotti]

/merge