test: assert minimum health after undercollateralised rebalance

Per PR review, add assertion that health after rebalance is at least 1.1 (minimum threshold)
to ensure protocol rebalances positions to a safe state.

Author: kgrgpg

cadence/tests/rebalance_undercollateralised_test.cdc

@@ -107,4 +107,8 @@ fun testRebalanceUndercollateralised() {
     log("Required paydown: ".concat(requiredPaydown.toString()))
     log("Expected debt: ".concat(expectedDebt.toString()))
     log("Actual debt: ".concat(actualDebt.toString()))
+
+    // Ensure health is at least the minimum threshold (1.1)
+    Test.assert(healthAfterRebalance >= 1.1,
+        message: "Health after rebalance should be at least the minimum (1.1) but was ".concat(healthAfterRebalance.toString()))
 }