Use Expect for clear expectations

Instead of this in tests

```v
module test

import ip { Ipv4 }

fn test_it_parses_ipv4_address() {
assert Ipv4.parse("192.168.1.1") or { Ipv4{} } == Ipv4{address: [u8(192), 168, 1, 1]!}
}
```

Use this

```v
module test

import khalyomede.expect { expect }
import ip { Ipv4 }

fn test_it_parses_ipv4_address() {
expect(Ipv4.parse("192.168.1.1") or { Ipv4{} }).to_be_equal_to(Ipv4{address: [u8(192), 168, 1, 1]!})
}
```