Use FVM in GitHub Actions and migrate to Flutter 3.32.4 (#641)

* feat: implement Flutter version management using FVM across CI workflows

* Flutter 3.29.3 + minor Package upgrades

* Replace deprecated `withOpacity`

* Upgrade major package versions without breaking changes.

* Disable unnecessary_async rule

Re-enable later

* New language version and automated fixes

- unnecessary_breaks
- unnecessary_underscore

* Update BUILDING.md to use fvm commands

* Add gitignore files for Android and iOS build artifacts

* Migrate iOS dependencies to Swift Package Manager

This is being done automatically by Flutter

* Flutter 3.32.4

* New sdk version

* docs: add IDE setup instructions and troubleshooting guide for FVM integration

pubspec.yaml

@@ -4,19 +4,20 @@ description: InvenTree stock management
 version: 0.18.1+98
 
 environment:
-  sdk: ">=2.19.5 <3.32.2"
+  sdk: ^3.8.1
 
 dependencies:
   adaptive_theme: ^3.3.0                  # Theme management (e.g. dark mode)
+  async: any
   audioplayers: ^6.1.0                    # Play audio files
   cached_network_image: ^3.3.1            # Download and cache remote images
   camera: ^0.11.1                         # Camera
   cupertino_icons: ^1.0.8
   currency_formatter: ^2.2.1              # Currency formatting
   datetime_picker_formfield: ^2.0.1       # Date / time picker
-  device_info_plus: ^10.1.2               # Information about the device
+  device_info_plus: ^11.4.0               # Information about the device
   dropdown_search: ^5.0.6                 # Dropdown autocomplete form fields
-  file_picker: ^8.1.2                     # Select files from the device
+  file_picker: ^10.1.4                    # Select files from the device
   flutter:
     sdk: flutter
   flutter_cache_manager: ^3.3.0