refactor(dart_frog_web_sockets): upgrade to Dart 2.19 and Very Good Analysis 4.0.0 (#536)

Author: felangel

packages/dart_frog_web_socket/analysis_options.yaml

@@ -1 +1 @@
-include: package:very_good_analysis/analysis_options.3.1.0.yaml
+include: package:very_good_analysis/analysis_options.4.0.0.yaml

packages/dart_frog_web_socket/pubspec.yaml

@@ -7,7 +7,7 @@ issue_tracker: https://github.com/VeryGoodOpenSource/dart_frog/issues
 documentation: https://dartfrog.vgv.dev/docs/overview
 
 environment:
-  sdk: ">=2.18.0 <3.0.0"
+  sdk: ">=2.19.0 <3.0.0"
 
 dependencies:
   dart_frog: ^0.3.0
@@ -18,4 +18,4 @@ dev_dependencies:
   http: ^0.13.5
   mocktail: ^0.3.0
   test: ^1.19.2
-  very_good_analysis: ^3.1.0
+  very_good_analysis: ^4.0.0