Refactor source layout

Introduce compat source sets and move all kotlin sources to the main directory

[no changelog]

src/main/kotlin/util/json/InstantAsLongSerializer.kt

@@ -0,0 +1,22 @@
+
+
+package moe.nea.firmament.util.json
+
+import kotlinx.datetime.Instant
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+object InstantAsLongSerializer : KSerializer<Instant> {
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("InstantAsLongSerializer", PrimitiveKind.LONG)
+    override fun deserialize(decoder: Decoder): Instant {
+        return Instant.fromEpochMilliseconds(decoder.decodeLong())
+    }
+
+    override fun serialize(encoder: Encoder, value: Instant) {
+        encoder.encodeLong(value.toEpochMilliseconds())
+    }
+}