Add larastan and fix static analysis issue

[alexkart]

This pull request includes updates to the composer.json file to add a new development dependency and an improvement to the type hinting in the FiltersExact class.

It looks like this project uses larastan for static analysis but there is no dev dependency for larastan.

Issue fixed:

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  Line   src/Filters/FiltersExact.php                                                                                                                                              
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  72     Parameter #1 $query of method Spatie\QueryBuilder\Filters\FiltersExact<TModelClass of Illuminate\Database\Eloquent\Model>::__invoke() expects                             
         Illuminate\Database\Eloquent\Builder<TModelClass of Illuminate\Database\Eloquent\Model>, Illuminate\Database\Eloquent\Builder<Illuminate\Database\Eloquent\Model> given.  
         🪪  argument.type                                                                                                                                                         
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