feat: store timeouts in database and log them ending

we have to do this because discord doesn't notify us when a timeout
ends naturally, only when a moderator removes it early.

Catalogger.Backend/Database/Migrations/003_store_timeouts.down.sql

@@ -0,0 +1 @@
+drop table timeouts;

Catalogger.Backend/Database/Migrations/003_store_timeouts.up.sql

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+create table timeouts (
+    id integer generated by default as identity primary key,
+    user_id bigint not null,
+    guild_id bigint not null,
+    moderator_id bigint,
+    until timestamptz not null
+);
+
+create unique index ix_timeouts_user_guild on timeouts (user_id, guild_id);

Catalogger.Backend/Database/Models/DiscordTimeout.cs

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+using NodaTime;
+
+namespace Catalogger.Backend.Database.Models;
+
+public class DiscordTimeout
+{
+    public int Id { get; init; }
+    public ulong UserId { get; init; }
+    public ulong GuildId { get; init; }
+    public ulong? ModeratorId { get; init; }
+    public Instant Until { get; init; }
+}

Catalogger.Backend/Database/Repositories/TimeoutRepository.cs

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+using Catalogger.Backend.Database.Models;
+using Dapper;
+using NodaTime;
+using Remora.Rest.Core;
+
+namespace Catalogger.Backend.Database.Repositories;
+
+public class TimeoutRepository(DatabaseConnection conn) : IDisposable, IAsyncDisposable
+{
+    public async Task<DiscordTimeout?> GetAsync(int id) =>
+        await conn.QueryFirstOrDefaultAsync<DiscordTimeout>(
+            "select * from timeouts where id = @id",
+            new { id }
+        );
+
+    public async Task<DiscordTimeout?> GetAsync(Snowflake guildId, Snowflake userId) =>
+        await conn.QueryFirstOrDefaultAsync<DiscordTimeout>(
+            "select * from timeouts where guild_id = @GuildId and user_id = @UserId",
+            new { GuildId = guildId.Value, UserId = userId.Value }
+        );
+
+    public async Task<List<DiscordTimeout>> GetAllAsync() =>
+        (await conn.QueryAsync<DiscordTimeout>("select * from timeouts order by id")).ToList();
+
+    public async Task<DiscordTimeout> SetAsync(
+        Snowflake guildId,
+        Snowflake userId,
+        Instant until,
+        Snowflake? moderatorId
+    ) =>
+        await conn.QueryFirstAsync<DiscordTimeout>(
+            """
+            insert into timeouts (user_id, guild_id, moderator_id, until)
+            values (@UserId, @GuildId, @ModeratorId, @Until)
+            on conflict (user_id, guild_id) do update
+            set moderator_id = @ModeratorId,
+                until = @Until
+            returning *
+            """,
+            new
+            {
+                UserId = userId.Value,
+                GuildId = guildId.Value,
+                ModeratorId = moderatorId?.Value,
+                Until = until,
+            }
+        );
+
+    public async Task<DiscordTimeout?> RemoveAsync(int id) =>
+        await conn.QueryFirstOrDefaultAsync<DiscordTimeout>(
+            "delete from timeouts where id = @id returning *",
+            new { id }
+        );
+
+    public async Task<DiscordTimeout?> RemoveAsync(Snowflake guildId, Snowflake userId) =>
+        await conn.QueryFirstOrDefaultAsync<DiscordTimeout>(
+            "delete from timeouts where guild_id = @GuildId and user_id = @UserId returning *",
+            new { GuildId = guildId.Value, UserId = userId.Value }
+        );
+
+    public void Dispose()
+    {
+        conn.Dispose();
+        GC.SuppressFinalize(this);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await conn.DisposeAsync();
+        GC.SuppressFinalize(this);
+    }
+}