feat(se): log default measurement set when none provided

Makes the implicit behavior of SE.run() transparent by logging the
measurement configuration used when the user does not supply a custom
Measurements object.

Author: cuihantao

andes/routines/se.py

@@ -260,6 +260,9 @@ def _default_measurements(self, seed=None):
         m.add_bus_voltage(sigma=0.01)
         m.add_bus_injection(sigma_p=0.02, sigma_q=0.03)
         m.generate_from_pflow(seed=seed)
+        logger.info("No measurements provided; using default set "
+                    "(all bus voltages + all bus injections, %d measurements).",
+                    m.nm)
         return m
 
     def _ensure_angle_reference(self):