feat(browser): implement modular browser management system

Adds a new browser management system with strategy pattern implementation:
- Introduces BrowserManager class with strategy pattern support
- Adds PlaywrightBrowserStrategy, CDPBrowserStrategy, and BuiltinBrowserStrategy
- Implements BrowserProfileManager for profile management
- Adds PagePoolConfig for browser page pooling
- Includes comprehensive test suite for all browser strategies

BREAKING CHANGE: Browser management has been moved to browser/ module. Direct usage of browser_manager.py and browser_profiler.py is deprecated.

crawl4ai/browser_profiler.py

@@ -555,7 +555,6 @@ class BrowserProfiler:
             else:
                 self.logger.error(f"Invalid choice. Please enter a number between 1 and {exit_option}.", tag="MENU")
 
-
     async def launch_standalone_browser(self, 
                                   browser_type: str = "chromium",
                                   user_data_dir: Optional[str] = None,