Add dynamic humidity calibration from temp offset

With the physical limitations of the SuperSensor, we were able to
compensate for the temperature differential due to internal heating from
the ESP, but this compensation was not being taken into account by the
humidity sensor.

Add a compensation factor based on the offset to ensure humidity
properly tracks the filtered temperature value.

supersensor.yaml

@@ -694,6 +694,20 @@ sensor:
       id: sht45_humidity
       accuracy_decimals: 1
       filters:
+        - lambda: |-
+            // Grab measured and corrected temperatures
+            float t_meas = id(sht45_temperature).state - id(temperature_offset);
+            float t_corr = id(sht45_temperature).state;
+            float rh_meas = x;
+
+            // Compute saturation vapor pressures (Magnus formula)
+            auto es = [](float T) { return 6.112 * exp((17.62 * T) / (243.12 + T)); };
+            float rh_corr = rh_meas * es(t_meas) / es(t_corr);
+
+            // Clamp to 0–100 %
+            if (rh_corr < 0) rh_corr = 0;
+            if (rh_corr > 100) rh_corr = 100;
+            return rh_corr + id(humidity_offset);
         - offset: !lambda return id(humidity_offset);
         - sliding_window_moving_average:
             window_size: 20