Update to support RestSharp v110.2.0

[ncosentino]

It seems as though there have been breaking API changes in RestSharp since this was last released.

When going into this constructor for a RedditClient: at Reddit.RedditClient..ctor(String appId, String refreshToken, String appSecret, String accessToken, String userAgent)

It seems as though there used to be a constructor for a RestSharp client with a single parameter: Method not found: 'Void RestSharp.RestClient..ctor(System.String)'.

I'm now torn because if I want to use this package, I need to downgrade RestSharp to some older version with high security vulnerabilities and break everything else in my app. Or... I need to go port all of the code in this library to meet the new RestSharp API.