Add a method to get total facets count

Nobody has claimed this yet.

The library doesn't have a method to get total count of facets.

Here is the code example, imagine an index `jobs` with columns `employer_id` and `employer_name`:
```
$client = new \Manticoresearch\Client();
$index = $client->index('jobs');

$query = new \Manticoresearch\Query\BoolQuery();
$query->must(new \Manticoresearch\Query\MatchQuery('amazon', 'employer_name'));

$search = $index->search($query);
$search->limit(0);
$search->offset($offset);
$search->facet('employer_id', null, $per_page);
$result = $search->get();

var_dump($result->getTotal()); // this returns total number of rows, not total number of facets
var_dump($result->getFacets()); // this returns facets
```

So, adding a method similar to this one could solve the issue:

```
$result->getTotalFacets()
```

Start by tracing the result object methods getTotal() and getFacets() from the search example, then inspect how facet data is returned by the index search. Add the requested total-facets accessor alongside those methods and verify that it reports the total facet count separately from the total row count.

Written by the indexing model from the issue text.