[Feature] Voice messages support (#2665)

src/Discord.Net.Rest/API/Common/Attachment.cs

@@ -24,5 +24,9 @@ namespace Discord.API
         public Optional<int> Width { get; set; }
         [JsonProperty("ephemeral")]
         public Optional<bool> Ephemeral { get; set; }
+        [JsonProperty("duration_secs")]
+        public Optional<double> DurationSeconds { get; set; }
+        [JsonProperty("waveform")]
+        public Optional<string> Waveform { get; set; }
     }
 }

src/Discord.Net.Rest/Entities/Messages/Attachment.cs

@@ -27,9 +27,13 @@ namespace Discord
         public string Description { get; }
         /// <inheritdoc />
         public string ContentType { get; }
+        /// <inheritdoc />
+        public string Waveform { get; }
+        /// <inheritdoc />
+        public double? Duration { get; }
 
         internal Attachment(ulong id, string filename, string url, string proxyUrl, int size, int? height, int? width,
-            bool? ephemeral, string description, string contentType)
+            bool? ephemeral, string description, string contentType, double? duration, string waveform)
         {
             Id = id;
             Filename = filename;
@@ -41,6 +45,8 @@ namespace Discord
             Ephemeral = ephemeral.GetValueOrDefault(false);
             Description = description;
             ContentType = contentType;
+            Duration = duration;
+            Waveform = waveform;
         }
         internal static Attachment Create(Model model)
         {
@@ -48,7 +54,9 @@ namespace Discord
                 model.Height.IsSpecified ? model.Height.Value : (int?)null,
                 model.Width.IsSpecified ? model.Width.Value : (int?)null,
                 model.Ephemeral.ToNullable(), model.Description.GetValueOrDefault(),
-                model.ContentType.GetValueOrDefault());
+                model.ContentType.GetValueOrDefault(),
+                model.DurationSeconds.IsSpecified ? model.DurationSeconds.Value : null,
+                model.Waveform.GetValueOrDefault(null));
         }
 
         /// <summary>