Replace references to NEU with Firmament

src/main/kotlin/moe/nea/firmament/util/TimeMark.kt

@@ -0,0 +1,15 @@
+package moe.nea.firmament.util
+
+import kotlin.time.Duration
+import kotlin.time.ExperimentalTime
+import kotlin.time.TimeSource
+
+@OptIn(ExperimentalTime::class)
+class TimeMark private constructor(private val timeMark: TimeSource.Monotonic.ValueTimeMark?) {
+    fun passedTime() = timeMark?.elapsedNow() ?: Duration.INFINITE
+
+    companion object {
+        fun now() = TimeMark(TimeSource.Monotonic.markNow())
+        fun farPast() = TimeMark(null)
+    }
+}