refactor(signalr): remove SignalR server & msgpack_lazer_api

Maybe we can make `msgpack_lazer_api` independent?

app/models/playlist.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from datetime import datetime
+
+from app.models.mods import APIMod
+
+from pydantic import BaseModel, Field
+
+
+class PlaylistItem(BaseModel):
+    id: int = Field(default=0, ge=-1)
+    owner_id: int
+    beatmap_id: int
+    beatmap_checksum: str = ""
+    ruleset_id: int = 0
+    required_mods: list[APIMod] = Field(default_factory=list)
+    allowed_mods: list[APIMod] = Field(default_factory=list)
+    expired: bool = False
+    playlist_order: int = 0
+    played_at: datetime | None = None
+    star_rating: float = 0.0
+    freestyle: bool = False