Make CameraPosition serializable for view-model saved state

lib/maplibre-compose/src/commonMain/kotlin/org/maplibre/compose/camera/CameraPosition.kt

@@ -1,6 +1,7 @@
 package org.maplibre.compose.camera
 
 import androidx.compose.runtime.Immutable
+import kotlinx.serialization.Serializable
 import org.maplibre.spatialk.geojson.Position
 
 /**
@@ -13,6 +14,7 @@ import org.maplibre.spatialk.geojson.Position
  * @param zoom Zoom level at target. A value in the range of `[0 .. 25.5]`
  */
 @Immutable
+@Serializable
 public data class CameraPosition(
   public val bearing: Double = 0.0,
   public val target: Position = Position(0.0, 0.0),

lib/maplibre-compose/src/commonTest/kotlin/org/maplibre/compose/camera/CameraPositionTest.kt

@@ -0,0 +1,31 @@
+package org.maplibre.compose.camera
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import org.maplibre.spatialk.geojson.Position
+
+class CameraPositionTest {
+  @Test
+  fun roundTripsCameraThroughJson() {
+    val expected =
+      CameraPosition(
+        bearing = 42.5,
+        target = Position(longitude = -122.675, latitude = 45.521, altitude = 12.0),
+        tilt = 30.0,
+        zoom = 13.0,
+      )
+
+    val encoded = Json.encodeToString(expected)
+
+    assertEquals(expected, Json.decodeFromString<CameraPosition>(encoded))
+  }
+
+  @Test
+  fun restoresOmittedFieldsToConstructorDefaults() {
+    val restored = Json.decodeFromString<CameraPosition>("{}")
+
+    assertEquals(CameraPosition(), restored)
+  }
+}