fix: Fix validation error. #MALNET-21 Fixed
fix: Fix validation error. #MALNET-21 Fixed

- Validation was using incorrect address (non-https one)
- Replaced old implementation with more modern HttpClient one

NinetailLabs/MAL.Net,NinetailLabs/MAL.Net---A-.net-API-for-MAL,NinetailLabs/MAL.Net---A-.net-API-for-MAL,NinetailLabs/MAL.Net