Remove nullable type declarations for RestGuild

Removed the nullable marker for the RestGuild type to ensure that a non-nullable RestGuild instance is always expected from GetGuildAsync method. This change increases type safety by preventing potential null reference exceptions.

Blink3.API/Controllers/GuildsController.cs

@@ -48,7 +48,7 @@ public async Task<ActionResult<IReadOnlyCollection<DiscordPartialChannel>>> GetC
         string cacheKey = $"guild_{id}_categories";
         IReadOnlyCollection<DiscordPartialChannel> categories = await _cachingService.GetOrAddAsync(cacheKey, async () =>
         {
-            RestGuild? guild = await _botClient.GetGuildAsync(id);
+            RestGuild guild = await _botClient.GetGuildAsync(id);
             IReadOnlyCollection<RestCategoryChannel>? categories = await guild.GetCategoryChannelsAsync();
             return categories
                 .OrderBy(c => c.Position)
@@ -80,7 +80,7 @@ public async Task<ActionResult<IReadOnlyCollection<DiscordPartialChannel>>> GetC
         string cacheKey = $"guild_{id}_channels";
         IReadOnlyCollection<DiscordPartialChannel> channels = await _cachingService.GetOrAddAsync(cacheKey, async () =>
         {
-            RestGuild? guild = await _botClient.GetGuildAsync(id);
+            RestGuild guild = await _botClient.GetGuildAsync(id);
             IReadOnlyCollection<RestTextChannel>? channels = await guild.GetTextChannelsAsync();
             return channels
                 .OrderBy(c => c.Position)