Required option for query params

Similar to `strict`, it would be handy with a `required` option that throws if the parameter is missing

```typescript
const searchParamsConfig = {
  count: parseAsInteger.withOptions({ required: true }),
}

const loadSearchParams = createLoader(searchParamsConfig )

// Expected:
const { count, contributors } = loadSearchParams(request, { strict: true })
//      count: number
```