Feature/phpstan generics for collection

[nvdbeek]

Fix #63 . Add phpstan and psalm generics for the collections.

[nvdbeek]

Made this final cause the following phpstan message:

  331    Unsafe usage of new static().                                                                                                                                                    
         💡 Consider making the class or the constructor final.   

Alternatively we can change new static() to new self() on line 367 and remove the unit tests that test this behaviour

[nusje2000]

Looks fine to me 👍

[nvdbeek]

Hi @aeviiq,

With the merge method is it possible to merge other collection instances into the collection with other instances. Whats your opinion about this? By merging this merge request it's no longer possible to merge 2 different instances into 1 collection.

Example:

/** @var PersonCollection<Person> $personCollection */
$personCollection = new PersonCollection();
$person = new Person();

$a = new Collection([$person]);
$a->merge($personCollection); // should work

/** @var ProductCollection<Product> $otherCollection */
$otherCollection = new ProductCollection();
$a->merge($otherCollection); // should give phpstan error (expects Person, ProductCollection given.)