Update flutter and devenv, set devenv to nixos-unstable

pubspec.yaml

@@ -43,8 +43,9 @@ dependencies:
   flutter_cache_manager: ^3.4.1
   flutter_secure_storage: ^9.2.2
   jwt_decoder: ^2.0.1
-  pdfrx: ^1.1.25
+  pdfrx: ^2.0.4
   logging: ^1.3.0
+  flutter_drawing_board: ^0.9.8
 
 dev_dependencies:
   flutter_test:
@@ -55,7 +56,7 @@ dev_dependencies:
   # activated in the `analysis_options.yaml` file located at the root of your
   # package. See that file for information about deactivating specific lint
   # rules and activating additional ones.
-  flutter_lints: ^5.0.0
+  flutter_lints: ^6.0.0
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec