Country code prefix fix for Number Insight (#302)

* Cast the country code prefix string to an integer in line with the expected return type

* do not cast to integer, reflect what comes back from API as leading zeroes might come back

Author: SecondeJK

src/Insights/Basic.php

@@ -62,7 +62,7 @@ public function getCountryName(): string
         return $this->data['country_name'];
     }
 
-    public function getCountryPrefix(): int
+    public function getCountryPrefix(): string
     {
         return $this->data['country_prefix'];
     }

test/Insights/BasicTest.php

@@ -63,7 +63,7 @@ public function basicTestProvider(): array
                 'country_code' => 'GB',
                 'country_code_iso3' => 'GBR',
                 'country_name' => 'United Kingdom',
-                'country_prefix' => 44,
+                'country_prefix' => '44',
         ];
 
         $basic1 = new Basic($inputBasic1['national_format_number']);