add tests and make several replacements/improvements

startup/plugin/src/jvmMain/kotlin/ServerPluginSerializer.kt

@@ -0,0 +1,23 @@
+package dev.inmo.micro_utils.startup.plugin
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.builtins.serializer
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+actual object ServerPluginSerializer : KSerializer<ServerPlugin> {
+    override val descriptor: SerialDescriptor
+    get() = String.serializer().descriptor
+
+    override fun deserialize(decoder: Decoder): ServerPlugin {
+        val kclass = Class.forName(decoder.decodeString()).kotlin
+        return (kclass.objectInstance ?: kclass.constructors.first { it.parameters.isEmpty() }.call()) as ServerPlugin
+    }
+
+    override fun serialize(encoder: Encoder, value: ServerPlugin) {
+        encoder.encodeString(
+            value::class.java.canonicalName
+        )
+    }
+}