Add turbine throttle mapping and back-pressure penalty

tests/test_turbine.py

@@ -6,10 +6,11 @@ from reactor_sim.turbine import Turbine
 
 def test_turbine_spools_toward_target_output():
     turbine = Turbine()
+    turbine.throttle = 1.0
     loop = CoolantLoopState(
         temperature_in=600.0,
         temperature_out=650.0,
-        pressure=6.0,
+        pressure=0.02,
         mass_flow_rate=20_000.0,
         steam_quality=0.9,
     )
@@ -20,14 +21,15 @@ def test_turbine_spools_toward_target_output():
         condenser_temperature=300.0,
     )
     target_electric = min(
-        turbine.rated_output_mw, 300.0 * turbine.mechanical_efficiency * turbine.generator_efficiency
+        turbine.rated_output_mw,
+        300.0 * turbine.mechanical_efficiency * turbine.generator_efficiency,
     )
 
-    dt = 5.0
+    dt = 1.0
     turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
     assert 0.0 < state.electrical_output_mw < target_electric
 
-    for _ in range(5):
+    for _ in range(60):
         turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
 
     assert state.electrical_output_mw == pytest.approx(target_electric, rel=0.05)