refactor: drop lolib, add own scheduler, inventory GUI and void generator

src/test/java/dev/loki/loparkour/scheduler/SchedulerTest.java

@@ -0,0 +1,22 @@
+package dev.loki.loparkour.scheduler;
+
+import org.bukkit.plugin.Plugin;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertSame;
+
+class SchedulerTest {
+
+    @Test
+    void testNoFoliaOnPlainJvm() {
+        assertFalse(Scheduler.isFolia(), "Folia server classes are absent in the test JVM");
+    }
+
+    @Test
+    void testInstancesAreCachedPerPlugin() {
+        final Plugin plugin = Mockito.mock(Plugin.class);
+        assertSame(Scheduler.get(plugin), Scheduler.get(plugin), "the same plugin must reuse one scheduler");
+    }
+}