wip: guild member remove

Catalogger.Backend/Cache/InMemoryCache/AuditLogCache.cs

@@ -0,0 +1,21 @@
+using System.Collections.Concurrent;
+using Remora.Discord.API;
+using Remora.Rest.Core;
+
+namespace Catalogger.Backend.Cache.InMemoryCache;
+
+public class AuditLogCache
+{
+    private readonly ConcurrentDictionary<(Snowflake, Snowflake), ModactionData> _kicks = new();
+    private readonly ConcurrentDictionary<(Snowflake, Snowflake), ModactionData> _bans = new();
+
+    public void SetKick(Snowflake guildId, string targetId, Snowflake moderatorId, Optional<string> reason)
+    {
+        if (!DiscordSnowflake.TryParse(targetId, out var targetUser))
+            throw new CataloggerError("Target ID was not a valid snowflake");
+
+        _kicks[(guildId, targetUser.Value)] = new ModactionData(moderatorId, reason.OrDefault());
+    }
+
+    public record struct ModactionData(Snowflake ModeratorId, string? Reason);
+}