feat(proxy): throw user-readable error on 413 when sending proxied attachments

Myriad/Rest/BaseRestClient.cs

@@ -262,6 +262,7 @@ public class BaseRestClient: IAsyncDisposable
             HttpStatusCode.Unauthorized => new UnauthorizedException(response, body, apiError),
             HttpStatusCode.NotFound => new NotFoundException(response, body, apiError),
             HttpStatusCode.Conflict => new ConflictException(response, body, apiError),
+            HttpStatusCode.RequestEntityTooLarge => new RequestEntityTooLargeException(response, body, apiError),
             HttpStatusCode.TooManyRequests => new TooManyRequestsException(response, body, apiError),
             _ => new UnknownDiscordRequestException(response, body, apiError)
         };

Myriad/Rest/Exceptions/DiscordRequestException.cs

@@ -61,6 +61,14 @@ public class BadRequestException: DiscordRequestException
     { }
 }
 
+public class RequestEntityTooLargeException: DiscordRequestException
+{
+    public RequestEntityTooLargeException(HttpResponseMessage response, string responseBody, DiscordApiError? apiError) : base(
+        response, responseBody, apiError)
+    { }
+}
+
+
 public class TooManyRequestsException: DiscordRequestException
 {
     public TooManyRequestsException(HttpResponseMessage response, string responseBody, DiscordApiError? apiError) :