[FR]: Unable to parse resource files existing in subdirectories

[birdycn]

Is there an existing issue for this?

• I have searched the existing issues

Describe the problem

I have such a directory：

- assets/icons/svg/system/a.svg
- assets/icons/svg/social/b.svg

I have made this configuration

flutter:
  generate: true
  uses-material-design: true
  assets:
    - assets/icons/svg/

flutter_gen:
  output: lib/gen
  assets:
    enabled: true
  integrations:
    flutter_svg: true
``

An empty file has been generated：

// dart format width=80

/// GENERATED CODE - DO NOT MODIFY BY HAND
/// *****************************************************
/// FlutterGen
/// *****************************************************

// coverage:ignore-file
// ignore_for_file: type=lint
// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import

class $AssetsIconsGen {
const $AssetsIconsGen();

/// Directory path: assets/icons/svg
$AssetsIconsSvgGen get svg => const $AssetsIconsSvgGen();
}

class $AssetsIconsSvgGen {
const $AssetsIconsSvgGen();
}

class Assets {
const Assets._();

static const $AssetsIconsGen icons = $AssetsIconsGen();
}

### Describe the solution

I hope to traverse subfiles

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct