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/purchase/purchase_stars.py

@@ -0,0 +1,53 @@
+"""
+Example: purchase Telegram Stars for a user.
+
+Amount must be an integer between 50 and 10 000 000.
+Set show_sender=False to send anonymously.
+Username can be "@username", "username", or "https://t.me/username".
+"""
+
+import asyncio
+
+from pyfragment import ConfigurationError, FragmentClient, UserNotFoundError
+from pyfragment.enums import PaymentMethod
+
+SEED = "word1 word2 ... word24"
+API_KEY = "YOUR_TONAPI_KEY"
+
+# Option A: extract cookies directly from your browser (no manual copy-paste needed)
+# COOKIES = get_cookies_from_browser("chrome").cookies  # or "firefox", "edge", "brave", ...
+
+# Option B: provide cookies manually
+COOKIES = {
+    "stel_ssid": "YOUR_STEL_SSID",
+    "stel_dt": "YOUR_STEL_DT",
+    "stel_token": "YOUR_STEL_TOKEN",
+    "stel_ton_token": "YOUR_STEL_TON_TOKEN",
+}
+
+USERNAME = "https://t.me/username"
+AMOUNT = 500  # 50–10 000 000 stars
+PAYMENT_METHOD = PaymentMethod.USDT_GRAM  # GRAM, USDT_GRAM, USDT_ETH, USDT_POL, USDC_ETH, USDC_BASE, USDC_POL
+
+
+async def main() -> None:
+    async with FragmentClient(seed=SEED, api_key=API_KEY, cookies=COOKIES) as client:
+        try:
+            result = await client.purchase_stars(
+                USERNAME,
+                amount=AMOUNT,
+                show_sender=True,
+                payment_method=PAYMENT_METHOD,
+            )
+        except UserNotFoundError:
+            print(f"User {USERNAME} was not found on fragment.com — check the username and try again.")
+            return
+        except ConfigurationError as e:
+            print(f"Invalid argument: {e}")
+            return
+
+    print(f"{result.amount} Stars successfully sent to {result.username} | tx: {result.transaction_id}")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())