feat: inherit signal on piping

Imagine:
```ts
const ac = new AbortController()
const {signal} = ac

const p1 = $({signal})`cmd`
const p2 = p1.pipe`cmd`.pipe`cmd`
```
It's required to pass the signal to the entire piped process chain

```ts
setTimeout(() => signal.abort(), 500)

const o2 = await p2 // Aborted
```

