Add support for endpoint checking prekey consistency.

core-util-jvm/src/main/java/org/signal/core/util/LongExtensions.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.core.util
+
+import java.nio.ByteBuffer
+
+/**
+ * Converts the long into [ByteArray].
+ */
+fun Long.toByteArray(): ByteArray {
+  return ByteBuffer
+    .allocate(Long.SIZE_BYTES)
+    .putLong(this)
+    .array()
+}