Update BASEFEE opcode hardcoded system value

[filip-parity]

When Solidity contracts execute block.basefee, they're reading the current transaction's gas price. However, the BASEFEE opcode handler in pallet-revive is ignoring the transaction-specific gas price.

In order to complete the task correctly, we need to update in polkadot-sdk line 88

from: interpreter.stack.push(crate::Pallet::<E::T>::evm_base_fee())?;
to: interpreter.stack.push(interpreter.ext.effective_gas_price())?;

This implementation would handle gas price that was set. If no gas price is set, the method has a fallback to the system default. This modification is also compliant with other opcodes (line 51, line 61, etc).