v1.2.0 - Add convenient methods

• Add compute_gas_fees(): utility function to compute gas fees
• Add build_transaction() method: It's now possible to build the full transaction i/o just the input data.
• Add fetch_permit2_allowance(): Easy way to check the current Permit2 allowed amount, expiration and nonce.
• Make verifying contract (Permit2) configurable (Thanks to @speedssr and @freereaper)
• Replace deprecated eth_account.encode_structured_data() with eth_account.messages.encode_typed_data()