ld: Add a delay before turning on LD PWR

- DAC output might not drop to 0V before PWR is being turned on
- Thus, it might drive nondeterministic current into the laser diode during pwr up

src/laser_diode/laser_diode.rs

@@ -121,6 +121,8 @@ impl LdDrive{
         let prev_i_set = self.settings.ld_drive_current;
         LdCurrentOutCtrlTimer::reset();        
         let _ = self.ctrl.set_i(ElectricCurrent::new::<milliampere>(0.0), Settings::LD_DRIVE_TRANSIMPEDANCE, Settings::DAC_OUT_V_MAX);
+        // Wait for the DAC to reset its voltage back to 0V
+        sleep(10);
         LdPwrExcProtector::pwr_on_and_arm_protection();
         // Wait for LD Power Supply to start up before driving current to laser diode
         sleep(30);