Add database table for storing lazer multiplayer room events

The goal of this table is to power display of multiplayer match history
for lazer rooms, e.g. #10455.

If you squint a bit, you'll notice that the table structure is
*extremely* similar to `osu_mp.events`, but to spell things out:

- `id` (PK)`: Self-explanatory.
- `room_id` (FK referencing `multiplayer_rooms`): Self-explanatory.
- `event_type`: Self-explanatory. Uses `string` rather than any explicit
  `enum` type for more flexibility and to reduce ceremony when adding
  new types in.
- `playlist_item_id` (FK referencing `multiplayer_playlist_items`,
  optional): Valid if `event_type` is `game_{started,aborted}`. Points
  at the game in question.
- `user_id` (FK referencing `phpbb_users`, optional): If the event can
  be associated with a user, it will be via this column.
- `{created,updated}_at`: Decided to just let laravel generate this one,
  although osu-web won't really be writing to this table, and I expect
  99.999% of records (if not all) to just contain the same value twice
  here. Not sure. Maybe this can be a single timestamp column or
  something, please advise.
- `event_detail`: This is somewhat new. The goal of this column is to
  store extra data, in particular in the case of `game_started` events.
  The specific data I want to store there are: the game mode at the time
  of starting (be it head-to-head, or team vs, or whichever), and also
  who's on what team in the room (if team vs). This information is
  currently not stored anywhere in the database; only the latest game
  mode is preserved, and the team composition is only stored in memory
  of the spectator server. This came up recently in
  ppy/osu#32680 (comment).

  Potentially, this could also be used to do things like store the
  users' total scores at the end of the match, which we presumably want
  to be 'frozen in time' at the point of match completion for archival
  purposes; because in lazer multiplayer scores just land in the
  `scores` table and will be treated the same way as solo scores, any
  potential rebalances could have a side effect of rewriting multiplayer
  match history if this sort of thing is not done preventatively. (The
  old `osu_mp` structure is immune from this because it completely
  mirrors score rows into its `game_scores` table.)

Note that currently the assumption is that this table will store events
for all rooms going forward, because there is no correspondent of the
`osu_mp.matches.keep_forever` flag anywhere for lazer multiplayer rooms.
Up for discussion as to whether we want to have one.

Author: bdach

database/migrations/2025_04_17_113658_create_multiplayer_room_events_table.php

@@ -0,0 +1,37 @@
+<?php
+
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the GNU Affero General Public License v3.0.
+// See the LICENCE file in the repository root for full licence text.
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('multiplayer_realtime_room_events', function (Blueprint $table) {
+            $table->bigIncrements('id');
+            $table->unsignedBigInteger('room_id');
+            $table->string('event_type');
+            $table->unsignedBigInteger('playlist_item_id')->nullable();
+            $table->unsignedInteger('user_id')->nullable();
+            $table->timestamps();
+            $table->json('event_detail')->nullable();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('multiplayer_realtime_room_events');
+    }
+};