chore: prefer named imports over default imports in examples

[0xumarkhatab]

Chapter 8 -> section 8.1 lacks import of stdError & Vm

Issue

There are multiple places where forge-std's components are used without importing them .

1. Lack of stdError and Vm import

A good practice is to use the pattern test_Revert[If|When]_Condition in combination with the [expectRevert](https://book.getfoundry.sh/cheatcodes/expect-revert.html) cheatcode (cheatcodes are explained in greater detail in the following [section](https://book.getfoundry.sh/forge/cheatcodes.html)). Also, other testing practices can be found in the [Tutorials section](https://book.getfoundry.sh/tutorials/best-practices.html). Now, instead of using testFail, you know exactly what reverted and with which error:

    function test_CannotSubtract43() public {
        vm.expectRevert(stdError.arithmeticError);
        testNumber -= 43;
    }

Impact

Beginners get confused when stdError is not found upon compilation of smart contracts because foundry demands explicit imports

Fix

Add following lines in the docs to import used components

import {Vm} from "forge-std/Vm.sol";
import {stdError} from "forge-std/StdError.sol";

[zerosnacks]

If you import as follows: import "forge-std/Test.sol";, as mentioned at the start, it will work

That said, I think we should modify the example code to reflect the best practices (e.g. named imports), especially as this is the entrypoint for beginners. We should also update the Solidity pragma to use pragma solidity ^0.8.13; to reflect the one generated by forge init.

@0xumarkhatab would you like to open a PR for this?

[zsskar]

Can I fix this little issue ?

[onbjerg]

Yes, feel free!

[zerosnacks]

Hi @zsskar would be great to get this fixed, do you still have time to work on it?

[zerosnacks]

Updated the title, resolving this by replacing default imports with named imports

#1298