use SQL's limit/offset pagination for nextIndex/maxCount requests (#185)

Instead of retrieving the entire list of items/characters/scores/etc. at once (and even store them in memory), use SQL's `LIMIT ... OFFSET ...` pagination so we only take what we need.

Currently only CHUNITHM uses this, but this will also affect maimai DX and O.N.G.E.K.I. once the PR is ready.

Also snuck in a fix for CHUNITHM/maimai DX's `GetUserRivalMusicApi` to respect the `userRivalMusicLevelList` sent by the client.

### How this works

Say we have a `GetUserCharacterApi` request:

```json
{
    "userId": 10000,
    "maxCount": 700,
    "nextIndex": 0
}
```

Instead of getting the entire character list from the database (which can be very large if the user force unlocked everything), add limit/offset to the query:

```python
select(character)
.where(character.c.user == user_id)
.order_by(character.c.id.asc())
.limit(max_count + 1)
.offset(next_index)
```

The query takes `maxCount + 1` items from the database to determine if there is more items than can be returned:

```python
rows = ...

if len(rows) > max_count:
    # return only max_count rows
    next_index += max_count
else:
    # return everything left
    next_index = -1
```

This has the benefit of not needing to load everything into memory (and also having to store server state, as seen in the [`SCORE_BUFFER` list](2274b42358/titles/chuni/base.py (L13)).)

Reviewed-on: Hay1tsme/artemis#185
Co-authored-by: beerpsi <beerpsi@duck.com>
Co-committed-by: beerpsi <beerpsi@duck.com>

core/data/alembic/env.py

@@ -1,14 +1,18 @@
 from __future__ import with_statement
 
 import asyncio
+import os
+from pathlib import Path
 import threading
 from logging.config import fileConfig
 
+import yaml
 from alembic import context
 from sqlalchemy import pool
 from sqlalchemy.engine import Connection
 from sqlalchemy.ext.asyncio import async_engine_from_config
 
+from core.config import CoreConfig
 from core.data.schema.base import metadata
 
 # this is the Alembic Config object, which provides
@@ -74,8 +78,18 @@ async def run_async_migrations() -> None:
     for override in overrides:
         ini_section[override] = overrides[override]
 
+    core_config = CoreConfig()
+    
+    with (Path("../../..") / os.environ["ARTEMIS_CFG_DIR"] / "core.yaml").open(encoding="utf-8") as f:
+        core_config.update(yaml.safe_load(f))
+
     connectable = async_engine_from_config(
-        ini_section, prefix="sqlalchemy.", poolclass=pool.NullPool
+        ini_section,
+        poolclass=pool.NullPool,
+        connect_args={
+            "charset": "utf8mb4",
+            "ssl": core_config.database.create_ssl_context_if_enabled(),
+        }
     )
 
     async with connectable.connect() as connection: