Detector Request: Implicit Typecast

### Describe the desired feature

It would be great to have a detector that checks for an implicit typecast in the code.

Example:

```solidity
uint64 a = 12345;
uint64 b = 1e18;

uint256 x = a * b;
```

This would revert since `a * b` happens in the `uint64` space then gets upcasted to `uint256` but won't be detected either by Solidity or Slither.