Refactor for GRAM (ex TON) integration

- Updated imports and references from TON to GRAM across multiple modules.
- Renamed functions and variables to reflect the change from TON to GRAM.
- Adjusted validation checks for top-up and recharge amounts to use GRAM limits.
- Modified error messages and exceptions to indicate GRAM instead of TON.
- Updated tests to ensure they reflect the new GRAM terminology and functionality.
- Introduced new constants for GRAM-related configurations.

examples/client/wallet_info.py

@@ -1,5 +1,5 @@
 """
-Example: fetch wallet address, state, and separate TON/USDT balances.
+Example: fetch wallet address, state, and separate GRAM (ex TON)/USDT balances.
 
 Cookies can be passed as a dict or as a JSON string.
 wallet_version defaults to "V5R1" — change to "V4R2" for older wallets.
@@ -34,7 +34,7 @@ async def main() -> None:
         wallet = await client.get_wallet()
         print(f"Address: {wallet.address}")
         print(f"State:   {wallet.state}")
-        print(f"Balance: {wallet.ton_balance} TON")
+        print(f"Balance: {wallet.gram_balance} GRAM (ex TON)")
         print(f"Balance: {wallet.usdt_balance} USDT")