refactor: Increment Dart SDK compatibility to <4.0.0; add example project (#883)

Author: mbfakourii

packages/dart/example/main.dart

@@ -0,0 +1,23 @@
+import '../lib/parse_server_sdk.dart';
+
+Future<void> main() async {
+  // Parse initialize
+  await Parse().initialize("keyApplicationId", "keyParseServerUrl",
+      clientKey: "keyParseClientKey",
+      debug: true,
+      liveQueryUrl: "keyLiveQueryUrl",
+      autoSendSessionId: true,
+      coreStore: CoreStoreMemoryImp());
+
+  // Set a ParseObject and save it
+  var dietPlan = ParseObject('DietPlan')
+    ..set('Name', 'Ketogenic')
+    ..set('Fat', 65);
+
+  var response = await dietPlan.save();
+
+  if (response.success) {
+    dietPlan = response.results?.first;
+    print("Response received successfully");
+  }
+}

packages/dart/pubspec.yaml

@@ -1,10 +1,10 @@
 name: parse_server_sdk
-description: The Dart SDK for Parse Platform (https://parseplatform.org)
+description: The Dart SDK to connect to Parse Server. Build your apps faster with Parse Platform, the complete application stack.
 version: 5.1.0
 homepage: https://github.com/parse-community/Parse-SDK-Flutter
 
 environment:
-  sdk: ">=2.18.0 <3.1.0"
+  sdk: ">=2.18.0 <4.0.0"
 
 dependencies:
   # Networking
@@ -32,3 +32,7 @@ dev_dependencies:
   build_runner: ^2.3.3
   mockito: ^5.3.2
   test: ^1.23.1
+
+screenshots:
+  - description: Parse Platform logo.
+    path: screenshots/logo.png