Hi!

I am getting an unexpected overflow on the following calculation:

```
contract;
use std::{
u256::U256,
};
abi MyContract {
fn test_function() -> bool;
}
impl MyContract for Contract {
fn test_function() -> bool {
let sum_u64_max = U256::from((0, 0, 0, u64::max())) + U256::from((0, 0, 0, u64::max()));
let will_overflow = sum_u64_max * sum_u64_max;
true
}
}
```

The number will_overflow = (2**64-1+2**64-1)*(2**64-1+2**64-1) which is << 2^256-1 returns the following error:

```
thread 'will_overflow' panicked at 'called `Result::unwrap()` on an `Err` value: RevertTransactionError("ArithmeticOverflow", [Call { id: 0000000000000000000000000000000000000000000000000000000000000000, to: 615aefc112c0d5bde30230cc4202e7b2e6e759d3139bdde8250d5ce0ad676f3b, amount: 0, asset_id: 0000000000000000000000000000000000000000000000000000000000000000, gas: 100000000, param1: 559005003, param2: 1, pc: 11624, is: 11624 }, Panic { id: 615aefc112c0d5bde30230cc4202e7b2e6e759d3139bdde8250d5ce0ad676f3b, reason: InstructionResult { reason: ArithmeticOverflow, instruction: Instruction { op: 45, ra: 16, rb: 18, rc: 19, rd: 17, imm06: 209, imm12: 1233, imm18: 74961, imm24: 4269265 } }, pc: 21320, is: 11624, contract_id: None }, ScriptResult { result: Panic, gas_used: 190373 }])', tests/harness.rs:47:6
```

Can this be an issue with the overflow checks ?