* Added validation for required command line options in the `CommandLine` class to ensure necessary parameters are provided.
* Updated `TestConfiguration` to store and expose the logging level from command line options.
* Refactored `BrowserstackApi` to improve method naming and added content type headers for API requests.
* Changed `SupportedBrowser` type to be exported for better accessibility.
* Updated `Page` and `SubscribingPage` classes to use a consistent browser import and improved constructor parameters.