Add plugin/theme download subcommands runnable before WordPress load

[Copilot]

This PR adds wp plugin download <slug> and wp theme download <slug> for deploy/automation flows where WordPress is not loaded. The commands resolve package metadata via WpOrgApi and download the ZIP directly.

• New before-load subcommands

  • Registered plugin download and theme download with when: before_wp_load.
  • Added dedicated command classes:
    • Plugin_Download_Command
    • Theme_Download_Command

• Download behavior

  • Fetches extension info from WordPress.org API (get_plugin_info / get_theme_info).
  • Downloads ZIP to a local path (default: current directory).
  • Supports:
    • --path=<path> (target directory)
    • --version=<version|dev> (builds version-specific package URL)
    • --force (overwrite existing destination file)
    • --insecure (TLS fallback behavior aligned with existing command patterns)

• Command metadata + coverage

  • Added new command entries to package command metadata in composer.json.
  • Added focused Behat feature coverage for both new commands:
    • features/extension-download.feature

wp plugin download debug-bar --skip-wordpress
wp theme download twentytwelve --skip-wordpress

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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