fix(simplex): raise ValueError instead of returning empty dict when max iterations reached

[unn-Known1]

Fixes #14584

Problem

The run_simplex() method in linear_programming/simplex.py silently returned an empty dict {} when the maximum iteration limit (Tableau.maxiter) was reached, with no indication of why it failed. This made it impossible for callers to distinguish between:

• A valid converging solution (returning {"P": 0.0})
• A cycling or unbounded problem that failed to converge

Solution

Modified run_simplex() to raise a descriptive ValueError when the maximum iterations are exhausted:

raise ValueError(
    "Simplex did not converge within "
    + str(max_iterations)
    + " iterations. The problem may be cycling or unbounded."
)

Testing

• All existing doctests pass
• The change is minimal and targeted (7 lines added, 1 line removed)

---

This contribution was developed with AI assistance.

[algorithms-keeper]

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