added lazy query support

fixed possible race condition of simultanous refetches of the same query

packages/example/lib/lazy_query.dart

@@ -0,0 +1,36 @@
+import 'package:fl_query/fl_query.dart';
+import 'package:flutter/material.dart';
+
+final lazyQueryJob = QueryJob<String, String>(
+    queryKey: "non_enabled_query",
+    enabled: false,
+    task: (queryKey, data) {
+      return Future.delayed(const Duration(milliseconds: 500),
+          () => "Hello from $queryKey with $data");
+    });
+
+class LazyQuery extends StatelessWidget {
+  const LazyQuery({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: QueryBuilder<String, String>(
+        job: lazyQueryJob,
+        externalData: "Love",
+        builder: (context, query) {
+          return Column(
+            children: [
+              Text("Query Data::: ${query.data ?? "Loading"}"),
+              ElevatedButton(
+                child: const Text("Fetch Query"),
+                onPressed: () => query.refetch(),
+              ),
+            ],
+          );
+        },
+      ),
+    );
+  }
+}

packages/example/lib/main.dart

@@ -1,6 +1,7 @@
 import 'dart:math';
 
 import 'package:example/another_component.dart';
+import 'package:example/lazy_query.dart';
 import 'package:example/query_with_external_data.dart';
 import 'package:fl_query/fl_query.dart';
 import 'package:flutter/material.dart';
@@ -35,7 +36,9 @@ final successJob = QueryJob<String, void>(
 
 final failedJob = QueryJob<String, void>(
   queryKey: "failure",
-  task: (queryKey, _) => Future.value("[$queryKey] Failed for unknown reason"),
+  task: (queryKey, _) => Random().nextBool()
+      ? Future.error("[$queryKey] Failed for unknown reason")
+      : Future.value("Success, you'll get slowly ${Random().nextInt(100)}!"),
 );
 
 class MyHomePage extends StatefulWidget {
@@ -90,8 +93,20 @@ class _MyHomePageState extends State<MyHomePage> {
                 job: failedJob,
                 externalData: null,
                 builder: (context, query) {
-                  if (query.hasError) return Text(query.error);
-                  return Text("Failure. You're a failure ${query.data}");
+                  return Row(
+                    children: [
+                      if (query.hasError)
+                        Text(
+                            "${query.error}. Retrying: ${query.retryAttempts}"),
+                      if (query.hasData)
+                        Text(
+                            "Success after ${query.retryAttempts}. Data: ${query.data}"),
+                      ElevatedButton(
+                        child: Text("Refetch ${query.queryKey}"),
+                        onPressed: () => query.refetch(),
+                      )
+                    ],
+                  );
                 },
               ),
             ],
@@ -106,6 +121,17 @@ class _MyHomePageState extends State<MyHomePage> {
               );
             },
           ),
+          const SizedBox(height: 10),
+          ElevatedButton(
+            child: const Text("Non Enabled Query Example"),
+            onPressed: () {
+              Navigator.of(context).push(
+                MaterialPageRoute(
+                  builder: (context) => const LazyQuery(),
+                ),
+              );
+            },
+          ),
           const AnotherComponent(),
         ],
       ),