Refactor cookie handling and service structure

- Removed the old CookieResult model from pyfragment.core.models and created a new one in pyfragment.services.cookies.models.
- Implemented get_cookies_from_browser function in pyfragment.services.cookies.service to extract cookies directly from supported browsers.
- Updated imports across various modules to reflect the new structure and removed unused imports.
- Cleaned up models in ads, anonymous_numbers, giveaways, marketplace, and purchases domains by removing unnecessary __all__ declarations.
- Added new example scripts for cookie extraction and various purchase functionalities.
- Consolidated constants into a new pyfragment.core.constants module for better organization.

examples/client/get_cookies.py

@@ -0,0 +1,33 @@
+"""
+Example: extract Fragment cookies directly from your browser.
+
+get_cookies_from_browser() reads the Fragment session cookies from a locally
+installed browser — no manual copy-paste required.
+
+Supported browsers: arc, brave, chrome, chromium, chromium_based, edge,
+                    firefox, firefox_based, librewolf, opera, opera_gx,
+                    safari, vivaldi.
+
+The returned CookieResult.cookies dict can be passed directly to FragmentClient.
+"""
+
+from pyfragment import CookieError, get_cookies_from_browser
+
+
+def main() -> None:
+    try:
+        result = get_cookies_from_browser("chrome")  # or "firefox", "edge", "brave", ...
+    except CookieError as e:
+        print(f"Could not read cookies: {e}")
+        return
+
+    print(f"Cookies expire: {result.expires}")
+    print(f"Keys found: {list(result.cookies.keys())}")
+
+    # Pass the extracted cookies directly to FragmentClient
+    # async with FragmentClient(seed=SEED, api_key=API_KEY, cookies=result.cookies) as client:
+    #     ...
+
+
+if __name__ == "__main__":
+    main()