refactor: split composeApp to client and ui

also renamed client.datasource to client.data, which made me realise
.gitignore was ignoring `data` and therefore some gtfsr source files
😭

shared/src/commonMain/kotlin/moe/lava/banksia/data/gtfsr/GtfsRealtime.kt

@@ -0,0 +1,12 @@
+package moe.lava.banksia.data.gtfsr
+
+import com.google.transit.realtime.FeedMessage
+
+abstract class GtfsRealtime(protected val data: FeedMessage) {
+    companion object {
+        inline fun <T: GtfsRealtime> parse(ctor: (FeedMessage) -> T, data: ByteArray): T {
+            val message = FeedMessage.ADAPTER.decode(data)
+            return ctor(message)
+        }
+    }
+}

shared/src/commonMain/kotlin/moe/lava/banksia/data/gtfsr/RealtimeVehiclePosition.kt

@@ -0,0 +1,22 @@
+package moe.lava.banksia.data.gtfsr
+
+import com.google.transit.realtime.FeedMessage
+import moe.lava.banksia.util.Point
+
+class RealtimeVehiclePositions(data: FeedMessage) : GtfsRealtime(data) {
+    private val positions = mutableMapOf<String, Point>()
+
+    init {
+        data.entity
+            .mapNotNull { ent ->
+                if (ent.vehicle?.position == null) return@mapNotNull null
+                ent.id to ent.vehicle.position.run {
+                    Point(latitude.toDouble(), longitude.toDouble())
+                }
+            }
+            .let { positions.putAll(it) }
+    }
+
+    fun getAll() = positions.toMap()
+    fun forTrip(tripId: String) = positions[tripId]
+}