feat: add SpeedCalculator to DistanceFilterProcessor for manual speed calculation

android/app/src/main/kotlin/dev/fiatcode/tracpulse/location/DistanceFilterProcessor.kt

@@ -18,6 +18,14 @@ class DistanceFilterProcessor {
     private var lastLongitude: Double? = null
     private var lastTimestamp: Long = 0
     private var lastHeading: Float? = null
+    private var speedCalculator: SpeedCalculator? = null
+
+    fun getCalculatedSpeed(location: Location): Float? {
+        if (speedCalculator == null) {
+            speedCalculator = SpeedCalculator()
+        }
+        return speedCalculator?.calculateSpeed(location.latitude, location.longitude, location.time)
+    }
 
     fun shouldAccept(location: Location, config: FilterConfig): Boolean {
         val now = System.currentTimeMillis()
@@ -72,6 +80,46 @@ class DistanceFilterProcessor {
         lastLongitude = null
         lastTimestamp = 0
         lastHeading = null
+        speedCalculator?.reset()
+    }
+
+    class SpeedCalculator {
+        private var lastLat: Double = 0.0
+        private var lastLon: Double = 0.0
+        private var lastTime: Long = 0
+
+        fun calculateSpeed(lat: Double, lon: Double, time: Long): Float? {
+            if (lastLat == 0.0 && lastLon == 0.0 && lastTime == 0L) {
+                lastLat = lat
+                lastLon = lon
+                lastTime = time
+                return null
+            }
+
+            val distance = haversineDistance(lastLat, lastLon, lat, lon)
+            val timeDelta = (time - lastTime) / 1000.0
+
+            if (timeDelta <= 0) {
+                lastLat = lat
+                lastLon = lon
+                lastTime = time
+                return null
+            }
+
+            val speed = (distance / timeDelta).toFloat()
+
+            lastLat = lat
+            lastLon = lon
+            lastTime = time
+
+            return speed
+        }
+
+        fun reset() {
+            lastLat = 0.0
+            lastLon = 0.0
+            lastTime = 0
+        }
     }
 
     companion object {