bimatrix.runLH / runtrace never detect runlemke failure (result is None check is dead since LcpResult) #23

Problem

Since #18 introduced LcpResult, lemke.runlemke always returns an LcpResult and never returns None: on secondary-ray termination it returns a result with success=False (lemke.py#L601-L609).

But bimatrix.runLH and bimatrix.runtrace still check for the old failure value:

• bimatrix.py#L165-L167 (runLH)
• bimatrix.py#L195-L197 (runtrace)

result = lemke.runlemke(lcp=lcp)
if result is None:
    raise RuntimeError("runlemke() failed to find a solution unexpectedly.")

So this RuntimeError can never be raised. If Lemke's algorithm ever fails, both methods silently return result.z[:-2] taken from a basis that is not an equilibrium, instead of reporting the failure. The docstrings added in #19 already document the RuntimeError, so the code should be brought in line with them.

Suggested fix

1. In runLH and runtrace, replace if result is None: with if not result.success:.
2. Add a unit test in tests/test_bimatrix_units.py for each method that makes runlemke return an unsuccessful LcpResult and checks that RuntimeError is raised. Ray termination shouldn't happen for well-formed bimatrix games, so the easiest way is to monkeypatch lemke.runlemke (pytest's monkeypatch fixture) to return e.g. LcpResult(success=False, ...).
3. Run pytest, ruff check and flake8 locally before pushing.

Best done on a fresh branch off main after #19 is merged, since #19 edits the docstrings right above these lines.