enforce values on network filter options when possible

Parsing the following and then converting it to content blocking syntax should _not_ cause a panic:

```
example.com$domain
```

Right now the filter is parsed but the content blocking conversion fails due to the missing domains.

This filter should fail at the parsing stage, and more generally, adblock-rust should always forbid filters from parsing when they have options which require associated values or options which cannot accept associated values.

The content blocking conversion part also should not cause panics for malformed filters.