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: #185
Co-authored-by: beerpsi <beerpsi@duck.com>
Co-committed-by: beerpsi <beerpsi@duck.com>

core/config.py

@@ -1,5 +1,9 @@
-import logging, os
-from typing import Any
+import logging
+import os
+import ssl
+from typing import Any, Union
+
+from typing_extensions import Optional
 
 class ServerConfig:
     def __init__(self, parent_config: "CoreConfig") -> None:
@@ -175,12 +179,60 @@ class DatabaseConfig:
         return CoreConfig.get_config_field(
             self.__config, "core", "database", "protocol", default="mysql"
         )
-        
+
     @property
-    def ssl_enabled(self) -> str:
+    def ssl_enabled(self) -> bool:
         return CoreConfig.get_config_field(
             self.__config, "core", "database", "ssl_enabled", default=False
         )
+        
+    @property
+    def ssl_cafile(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_cafile", default=None
+        )
+
+    @property
+    def ssl_capath(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_capath", default=None
+        )
+
+    @property
+    def ssl_cert(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_cert", default=None
+        )
+    
+    @property
+    def ssl_key(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_key", default=None
+        )
+    
+    @property
+    def ssl_key_password(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_key_password", default=None
+        )
+
+    @property
+    def ssl_verify_identity(self) -> bool:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_verify_identity", default=True
+        )
+    
+    @property
+    def ssl_verify_cert(self) -> Optional[Union[str, bool]]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_verify_cert", default=None
+        )
+
+    @property
+    def ssl_ciphers(self) -> Optional[str]:
+        return CoreConfig.get_config_field(
+            self.__config, "core", "database", "ssl_ciphers", default=None
+        )
 
     @property
     def sha2_password(self) -> bool:
@@ -208,6 +260,53 @@ class DatabaseConfig:
             self.__config, "core", "database", "memcached_host", default="localhost"
         )
 
+    def create_ssl_context_if_enabled(self):
+        if not self.ssl_enabled:
+            return
+
+        no_ca = (
+            self.ssl_cafile is None
+            and self.ssl_capath is None
+        )
+
+        ctx = ssl.create_default_context(
+            cafile=self.ssl_cafile,
+            capath=self.ssl_capath,
+        )
+        ctx.check_hostname = not no_ca and self.ssl_verify_identity
+
+        if self.ssl_verify_cert is None:
+            ctx.verify_mode = ssl.CERT_NONE if no_ca else ssl.CERT_REQUIRED
+        elif isinstance(self.ssl_verify_cert, bool):
+            ctx.verify_mode = (
+                ssl.CERT_REQUIRED
+                if self.ssl_verify_cert
+                else ssl.CERT_NONE
+            )
+        elif isinstance(self.ssl_verify_cert, str):
+            value = self.ssl_verify_cert.lower()
+
+            if value in ("none", "0", "false", "no"):
+                ctx.verify_mode = ssl.CERT_NONE
+            elif value == "optional":
+                ctx.verify_mode = ssl.CERT_OPTIONAL
+            elif value in ("required", "1", "true", "yes"):
+                ctx.verify_mode = ssl.CERT_REQUIRED
+            else:
+                ctx.verify_mode = ssl.CERT_NONE if no_ca else ssl.CERT_REQUIRED
+        
+        if self.ssl_cert:
+            ctx.load_cert_chain(
+                self.ssl_cert,
+                self.ssl_key,
+                self.ssl_key_password,
+            )
+        
+        if self.ssl_ciphers:
+            ctx.set_ciphers(self.ssl_ciphers)
+        
+        return ctx
+
 class FrontendConfig:
     def __init__(self, parent_config: "CoreConfig") -> None:
         self.__config = parent_config