feat(windows): add post-package command option for Windows packaging

[annd22]

Add --post-package-windows-cmd option to execute custom commands between
build and package steps for Windows platform. This enables custom file
operations (like code signing) on the built executable before packaging.

Changes:

• Add new CLI option --post-package-windows-cmd in command_package.dart
• Implement command execution logic in unified_distributor.dart
• Add proper error handling and logging for custom command execution

Example usage:
fastforge package --platform windows --targets exe --post-package-windows-cmd="call ./sign-file.bat"

[annd22]

This pull request is for: #272

[lijy91]

Hi @annd22, thanks for your contribution!

This PR has been superseded by #342 which implements a more general prepackage/postpackage hooks system that:

• Works for all platforms (not just Windows)
• Supports both pre and post hooks
• Can be configured via YAML (distribute_options.yaml) or CLI flags (--hook-pre/--hook-post)
• Supports multiple commands (not just a single string)
• Provides rich environment variables (PLATFORM, BUILD_OUTPUT_DIRECTORY, etc.)

So instead of:

fastforge package --platform windows --targets exe --post-package-windows-cmd="call ./sign-file.bat"

You can now do:

fastforge package --platform windows --targets exe --hook-post "call ./sign-file.bat"

Or via YAML:

package:
  platform: windows
  target: exe
  hooks:
    post: call ./sign-file.bat

Please check out #342 for details. Thanks again! 🙏