feature: add StartedAt, EndsAt, Elapsed and Remaining to SpotifyGame. (#1414)

* Fixed GetUsersAsync to use MaxUsersPerBatch const as limit instead of MaxMessagesPerBatch.

Requests are now returning up to 1000 guild user entities instead of the previous 100.

* Added StartedAt and EndsAt timespans for SpotifyGame.
They make it possible to expose track's Elapsed and Remaining properties.

* Moved Duration to be initialized within model construction.

* Updated StartedAt and EndsAt comments.

src/Discord.Net.Core/Entities/Activities/SpotifyGame.cs

@@ -31,6 +31,23 @@ namespace Discord
         ///     A string containing the name of the song (e.g. <c>Lonely Together (feat. Rita Ora)</c>).
         /// </returns>
         public string TrackTitle { get; internal set; }
+
+        /// <summary>
+        ///     Gets the date when the track started playing.
+        /// </summary>
+        /// <returns>
+        ///     A <see cref="DateTimeOffset"/> containing the start timestamp of the song.
+        /// </returns>
+        public DateTimeOffset? StartedAt { get; internal set; }
+
+        /// <summary>
+        ///     Gets the date when the track ends.
+        /// </summary>
+        /// <returns>
+        ///     A <see cref="DateTimeOffset"/> containing the finish timestamp of the song.
+        /// </returns>
+        public DateTimeOffset? EndsAt { get; internal set; }
+
         /// <summary>
         ///     Gets the duration of the song.
         /// </summary>
@@ -39,6 +56,22 @@ namespace Discord
         /// </returns>
         public TimeSpan? Duration { get; internal set; }
 
+        /// <summary>
+        ///     Gets the elapsed duration of the song.
+        /// </summary>
+        /// <returns>
+        ///     A <see cref="TimeSpan"/> containing the elapsed duration of the song.
+        /// </returns>
+        public TimeSpan? Elapsed => DateTimeOffset.UtcNow - StartedAt;
+
+        /// <summary>
+        ///     Gets the remaining duration of the song.
+        /// </summary>
+        /// <returns>
+        ///     A <see cref="TimeSpan"/> containing the remaining duration of the song.
+        /// </returns>
+        public TimeSpan? Remaining => EndsAt - DateTimeOffset.UtcNow;
+
         /// <summary>
         ///     Gets the track ID of the song.
         /// </summary>

src/Discord.Net.WebSocket/Extensions/EntityExtensions.cs

@@ -38,6 +38,8 @@ namespace Discord.WebSocket
                     AlbumTitle = albumText,
                     TrackTitle = model.Details.GetValueOrDefault(),
                     Artists = model.State.GetValueOrDefault()?.Split(';').Select(x=>x?.Trim()).ToImmutableArray(),
+                    StartedAt = timestamps?.Start,
+                    EndsAt = timestamps?.End,
                     Duration = timestamps?.End - timestamps?.Start,
                     AlbumArtUrl = albumArtId != null ? CDN.GetSpotifyAlbumArtUrl(albumArtId) : null,
                     Type = ActivityType.Listening,