mc_hover_thrust_estimator: validity flag and other small improvements/fixes

- track and publish validity based on hover thrust variance, innovation test ratio, and hysteresis
 - only publish on actual updates or becoming inactive
 - fix dt (previous timestamp wasn't being saved)
 - use local position timestamp (corresponding) to accel data rather than current time to avoid unnecessary timing jitter
 - check local position validity before using
 - mc_hover_thrust_estimator: move from wq:lp_default -> wq:nav_and_controllers to ensure the hover thrust estimator runs after the position controller and uses the same vehicle_local_position data
 - land_detector: check hover thrust estimate validity and adjust low throttle thresholds if hover thrust is available
 - mc_pos_control: only use hover thrust estimate if valid

src/modules/land_detector/MulticopterLandDetector.cpp

@@ -106,7 +106,11 @@ void MulticopterLandDetector::_update_topics()
 		hover_thrust_estimate_s hte;
 
 		if (_hover_thrust_estimate_sub.update(&hte)) {
-			_params.hoverThrottle = hte.hover_thrust;
+			if (hte.valid) {
+				_params.hoverThrottle = hte.hover_thrust;
+			}
+
+			_hover_thrust_estimate_valid = hte.valid;
 		}
 	}
 }
@@ -182,9 +186,9 @@ bool MulticopterLandDetector::_get_ground_contact_state()
 	}
 
 
-	// low thrust: 30% of throttle range between min and hover
-	const float sys_low_throttle = _params.minThrottle + (_params.hoverThrottle - _params.minThrottle) * 0.3f;
-
+	// low thrust: 30% of throttle range between min and hover, relaxed to 60% if hover thrust estimate available
+	const float thr_pct_hover = _hover_thrust_estimate_valid ? 0.6f : 0.3f;
+	const float sys_low_throttle = _params.minThrottle + (_params.hoverThrottle - _params.minThrottle) * thr_pct_hover;
 	bool ground_contact = (_actuator_controls_throttle <= sys_low_throttle);
 
 	// if we have a valid velocity setpoint and the vehicle is demanded to go down but no vertical movement present,

src/modules/land_detector/MulticopterLandDetector.h

@@ -114,6 +114,7 @@ private:
 
 	bool _flag_control_climb_rate_enabled{false};
 	bool _hover_thrust_initialized{false};
+	bool _hover_thrust_estimate_valid{false};
 
 	float _actuator_controls_throttle{0.f};