fix: add CallDurationHelper to keep track of call duration

app/src/main/kotlin/com/simplemobiletools/dialer/helpers/CallDurationHelper.kt

@@ -0,0 +1,32 @@
+package com.simplemobiletools.dialer.helpers
+
+import java.util.Timer
+import java.util.TimerTask
+
+class CallDurationHelper {
+    private var callTimer = Timer()
+    private var callDuration = 0
+    private var callback: ((durationSecs: Int) -> Unit)? = null
+
+    fun onDurationChange(callback: (durationSecs: Int) -> Unit) {
+        this.callback = callback
+    }
+
+    fun start() {
+        try {
+            callTimer.scheduleAtFixedRate(getTimerUpdateTask(), 1000, 1000)
+        } catch (ignored: Exception) {
+        }
+    }
+
+    fun cancel() {
+        callTimer.cancel()
+    }
+
+    private fun getTimerUpdateTask() = object : TimerTask() {
+        override fun run() {
+            callDuration++
+            callback?.invoke(callDuration)
+        }
+    }
+}