refactor(android): add shared formatDuration + ms/sec conversion helpers

android/app/src/main/java/com/fabledsword/minstrel/shared/Formatting.kt

@@ -0,0 +1,23 @@
+package com.fabledsword.minstrel.shared
+
+const val MILLIS_PER_SECOND = 1000
+
+private const val SECONDS_PER_MINUTE = 60
+
+/**
+ * Formats [seconds] as m:ss. Returns [zero] when [seconds] <= 0 — pass
+ * "--:--" for unknown track durations, "0:00" (default) for playback
+ * position/duration. The single mm:ss formatter for the client.
+ */
+fun formatDuration(seconds: Int, zero: String = "0:00"): String =
+    if (seconds <= 0) {
+        zero
+    } else {
+        "%d:%02d".format(seconds / SECONDS_PER_MINUTE, seconds % SECONDS_PER_MINUTE)
+    }
+
+fun Int.secondsToMillis(): Int = this * MILLIS_PER_SECOND
+
+fun Int.millisToSeconds(): Int = this / MILLIS_PER_SECOND
+
+fun Long.millisToSeconds(): Int = (this / MILLIS_PER_SECOND).toInt()