feat: Allow re-run of RelicApp

lib/src/adapter/io/io_adapter.dart

@@ -99,7 +99,7 @@ class IOAdapter extends Adapter {
   }
 
   @override
-  Future<void> close() => _server.close(force: true);
+  Future<void> close() => _server.close();
 
   @override
   ConnectionsInfo get connectionsInfo {

lib/src/router/relic_app.dart

@@ -56,7 +56,9 @@ final class RelicApp implements RelicRouter {
 
   Future<void> close() async {
     await _reloadSubscription?.cancel();
+    _reloadSubscription = null;
     await _server?.close();
+    _server = null;
   }
 
   Future<void> _init() async {

test/router/relic_app_test.dart

@@ -46,6 +46,31 @@ void main() {
       await app.close();
     });
 
+    test('Given a RelicApp, '
+        'when calling serve twice, '
+        'then it fails the second time', () async {
+      final app =
+          RelicApp()..any('/', (final ctx) => ctx.respond(Response.ok()));
+
+      await app.serve(port: 0);
+      await expectLater(app.serve(port: 0), throwsStateError);
+
+      await app.close();
+    });
+
+    test('Given a RelicApp, '
+        'when calling serve, close, serve, '
+        'then it succeeds', () async {
+      final app =
+          RelicApp()..any('/', (final ctx) => ctx.respond(Response.ok()));
+
+      await app.serve(port: 0);
+      await app.close();
+      await expectLater(app.serve(port: 0), completes);
+
+      await app.close();
+    });
+
     test('Given a RelicApp, '
         'when hot-reloading isolate, '
         'then it is rebuild', () async {