switch to signed-first approach

It turns out signed math is more performant

src/commonTest/kotlin/com/infendro/bytes/long/Conversion.kt

@@ -0,0 +1,37 @@
+package com.infendro.bytes.long
+
+import com.infendro.bytes.ByteOrder.LITTLE_ENDIAN
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+
+class LongConversionTest {
+    @Test
+    fun toByteArray() {
+        val expected = arrayOf(
+            byteArrayOf(0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78),
+            byteArrayOf(0x78, 0x56, 0x34, 0x12, 0x78, 0x56, 0x34, 0x12),
+        )
+        val actual = arrayOf(
+            0x1234567812345678L.toByteArray(),
+            0x1234567812345678L.toByteArray(LITTLE_ENDIAN),
+        )
+        for (i in 0..1) {
+            assertContentEquals(expected[i], actual[i])
+        }
+    }
+
+    @Test
+    fun toUByteArray() {
+        val expected = arrayOf(
+            ubyteArrayOf(0x12U, 0x34U, 0x56U, 0x78U, 0x12U, 0x34U, 0x56U, 0x78U),
+            ubyteArrayOf(0x78U, 0x56U, 0x34U, 0x12U, 0x78U, 0x56U, 0x34U, 0x12U),
+        )
+        val actual = arrayOf(
+            0x1234567812345678L.toUByteArray(),
+            0x1234567812345678L.toUByteArray(LITTLE_ENDIAN),
+        )
+        for (i in 0..1) {
+            assertContentEquals(expected[i], actual[i])
+        }
+    }
+}