Function isNzbUrl

isNzbUrl(url: string): boolean
Tells whether a web URL points at an NZB document, judged by its path.
Parameters
- url: string
  A URL string.
Returns boolean
True when the URL parses and its path ends in .nzb.
Example
```
isNzbUrl('https://indexer.example/get/123.nzb'); // true
isNzbUrl('https://example.com/index.html'); // false
```