refactor: CoordinateUtils.get_coordinates_from_mic_e uses guarded clauses

- get_coordinates_from_mic_e: replace two inline `if direction == ...`
  rebinds with a reusable apply_hemisphere_sign/3 helper; the final
  range check becomes maybe_return_coords/2 with a guarded clause that
  yields {lat, lon} or {nil, nil}.
- has_position_data?: the boolean short-circuit collapses from an
  explicit if/else to a single `or` expression.

All 37 CoordinateUtils tests (4 properties) still pass.

lib/aprsme_web/live/shared/coordinate_utils.ex

@@ -33,13 +33,31 @@ defmodule AprsmeWeb.Live.Shared.CoordinateUtils do
   """
   @spec get_coordinates_from_mic_e(MicE.t()) :: {number() | nil, number() | nil}
   def get_coordinates_from_mic_e(mic_e) do
-    lat = mic_e.lat_degrees + mic_e.lat_minutes / 60.0 + mic_e.lat_fractional / 6000.0
-    lat = if mic_e.lat_direction == :south, do: -lat, else: lat
-    lon = mic_e.lon_degrees + mic_e.lon_minutes / 60.0 + mic_e.lon_fractional / 6000.0
-    lon = if mic_e.lon_direction == :west, do: -lon, else: lon
-    if lat >= -90 && lat <= 90 && lon >= -180 && lon <= 180, do: {lat, lon}, else: {nil, nil}
+    lat =
+      apply_hemisphere_sign(
+        mic_e.lat_degrees + mic_e.lat_minutes / 60.0 + mic_e.lat_fractional / 6000.0,
+        mic_e.lat_direction,
+        :south
+      )
+
+    lon =
+      apply_hemisphere_sign(
+        mic_e.lon_degrees + mic_e.lon_minutes / 60.0 + mic_e.lon_fractional / 6000.0,
+        mic_e.lon_direction,
+        :west
+      )
+
+    maybe_return_coords(lat, lon)
   end
 
+  # Negate the value when the hemisphere indicator matches the negative axis.
+  defp apply_hemisphere_sign(value, direction, negative) when direction == negative, do: -value
+  defp apply_hemisphere_sign(value, _direction, _negative), do: value
+
+  defp maybe_return_coords(lat, lon) when lat >= -90 and lat <= 90 and lon >= -180 and lon <= 180, do: {lat, lon}
+
+  defp maybe_return_coords(_lat, _lon), do: {nil, nil}
+
   @doc """
   Check if packet has position data in any format.
   """
@@ -48,11 +66,7 @@ defmodule AprsmeWeb.Live.Shared.CoordinateUtils do
     lat = Map.get(packet, :lat) || Map.get(packet, "lat")
     lon = Map.get(packet, :lon) || Map.get(packet, "lon")
 
-    if has_direct_coordinates?(lat, lon) do
-      true
-    else
-      has_position_in_data_extended?(packet)
-    end
+    has_direct_coordinates?(lat, lon) or has_position_in_data_extended?(packet)
   end
 
   @doc """