Re-add rate limit margins

DiscordChatExporter.Core/Utils/Extensions/TimeSpanExtensions.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace DiscordChatExporter.Core.Utils.Extensions;
+
+public static class TimeSpanExtensions
+{
+    public static TimeSpan Clamp(this TimeSpan value, TimeSpan min, TimeSpan max)
+    {
+        if (value < min)
+            return min;
+
+        if (value > max)
+            return max;
+
+        return value;
+    }
+}

DiscordChatExporter.Core/Utils/Http.cs

@@ -41,7 +41,10 @@ public static class Http
                 {
                     // If rate-limited, use retry-after header as the guide
                     if (result.Result.Headers.RetryAfter?.Delta is { } retryAfter)
-                        return retryAfter;
+                    {
+                        // Add some buffer just in case
+                        return retryAfter + TimeSpan.FromSeconds(1);
+                    }
 
                     return TimeSpan.FromSeconds(Math.Pow(2, i) + 1);
                 },