Address final-review findings on #1067

- MinimumDiscretePlanarInverseKinematics: simplify complexity
  string from "num_links * total_configurations" to
  "total_configurations" so it matches issue #994's stated
  O(prod_{j=1}^n m_j) baseline literally (the extra num_links
  factor was per-config feasibility-check work, not configs).

- MinimumCostCirculation: add test_minimum_cost_circulation_issue_example_1030
  that constructs issue #1030's verbatim 2-vertex example (arcs
  0->1 cap=2 cost=3 and 1->0 cap=1 cost=-5, optimum -2). The
  existing richer 3-vertex canonical instance is kept as the
  primary discriminator.

Author: isPANN

src/models/misc/minimum_discrete_planar_inverse_kinematics.rs

@@ -247,7 +247,7 @@ impl Problem for MinimumDiscretePlanarInverseKinematics {
 }
 
 crate::declare_variants! {
-    default MinimumDiscretePlanarInverseKinematics => "num_links * total_configurations",
+    default MinimumDiscretePlanarInverseKinematics => "total_configurations",
 }
 
 #[cfg(feature = "example-db")]

src/unit_tests/models/graph/minimum_cost_circulation.rs

@@ -132,6 +132,27 @@ fn test_minimum_cost_circulation_negative_cycle_beats_zero() {
     assert_eq!(problem.evaluate(&[0, 0]), Min(Some(0)));
 }
 
+#[test]
+fn test_minimum_cost_circulation_issue_example_1030() {
+    // Verbatim instance from issue #1030: vertices {0,1}, arcs
+    //   0->1 cap=2 cost= 3
+    //   1->0 cap=1 cost=-5
+    // Bottleneck is the back-arc (cap=1), so the optimum sends one unit
+    // around the cycle: cost = 1*3 + 1*(-5) = -2.
+    let problem = MinimumCostCirculation::new(
+        DirectedGraph::new(2, vec![(0, 1), (1, 0)]),
+        vec![2, 1],
+        vec![3, -5],
+    );
+    let solver = BruteForce::new();
+    let witness = solver
+        .find_witness(&problem)
+        .expect("instance must be feasible");
+    assert_eq!(witness, vec![1, 1]);
+    assert_eq!(problem.total_cost(&witness), -2);
+    assert_eq!(problem.evaluate(&[0, 0]), Min(Some(0)));
+}
+
 #[test]
 fn test_minimum_cost_circulation_serialization() {
     let problem = canonical_instance();