Fix SCPI server response handling and add TEMP:RAMP command

- Revert server to only send responses for non-empty strings
  Per SCPI protocol: successful commands with no output send nothing
- Add TEMP:RAMP command support to thermal chamber simulator
- Fixes test_multiple_commands and test_physics_engine_integration

TCP server integration tests now passing (8/8).
TempCo integration tests still need work due to async/sync mixing.

src/py_dvt_ate/simulation/virtual/chamber.py

@@ -26,6 +26,8 @@ class ThermalChamberSim(BaseInstrument):
         TEMP:SETPOINT?         - Query current setpoint
         TEMP:ACTUAL?           - Query actual chamber temperature
         TEMP:STAB?             - Query temperature stability (1=stable, 0=settling)
+        TEMP:RAMP <value>      - Set temperature ramp rate in degrees C/min
+        TEMP:RAMP?             - Query current ramp rate
 
     Attributes:
         manufacturer: "PyDVTATE"
@@ -47,6 +49,7 @@ class ThermalChamberSim(BaseInstrument):
             physics_engine: Reference to physics engine for temperature state.
         """
         self._setpoint = 25.0  # Default setpoint
+        self._ramp_rate = 10.0  # Default ramp rate in degrees C/min
         super().__init__(physics_engine)
 
     def _setup_commands(self) -> None:
@@ -54,10 +57,12 @@ class ThermalChamberSim(BaseInstrument):
         self.register_command("TEMP:SETPOINT", self._handle_temp_setpoint)
         self.register_command("TEMP:ACTUAL", self._handle_temp_actual)
         self.register_command("TEMP:STAB", self._handle_temp_stab)
+        self.register_command("TEMP:RAMP", self._handle_temp_ramp)
 
     def reset(self) -> None:
         """Reset chamber to default state."""
         self._setpoint = 25.0
+        self._ramp_rate = 10.0
         if self._physics_engine is not None:
             self._physics_engine.set_chamber_setpoint(self._setpoint)
 
@@ -141,3 +146,36 @@ class ThermalChamberSim(BaseInstrument):
         if error <= self.STABILITY_THRESHOLD:
             return "1"
         return "0"
+
+    def _handle_temp_ramp(self, command: SCPICommand) -> str:
+        """Handle TEMP:RAMP command/query.
+
+        Args:
+            command: Parsed SCPI command.
+
+        Returns:
+            Ramp rate value for query, empty string for set command.
+
+        Raises:
+            ValueError: If ramp rate argument is invalid.
+        """
+        if command.is_query:
+            return f"{self._ramp_rate:.2f}"
+
+        # Set command requires one argument
+        if not command.arguments:
+            raise ValueError("TEMP:RAMP requires a value")
+
+        try:
+            ramp_rate = float(command.arguments[0])
+        except ValueError as err:
+            raise ValueError(f"Invalid ramp rate value: {command.arguments[0]}") from err
+
+        if ramp_rate <= 0:
+            raise ValueError("Ramp rate must be positive")
+
+        self._ramp_rate = ramp_rate
+        # Note: Simulator doesn't currently model ramp rate dynamics
+        # The value is stored but not used in physics calculations
+
+        return ""