refactor(database): use a new 'On-Demand' design (#86)

Technical Details: https://blog.mxgame.top/2025/11/22/An-On-Demand-Design-Within-SQLModel/

app/database/search_beatmapset.py

@@ -0,0 +1,13 @@
+from . import beatmap  # noqa: F401
+from .beatmapset import BeatmapsetModel
+
+from sqlmodel import SQLModel
+
+SearchBeatmapset = BeatmapsetModel.generate_typeddict(("beatmaps.max_combo", "pack_tags"))
+
+
+class SearchBeatmapsetsResp(SQLModel):
+    beatmapsets: list[SearchBeatmapset]  # pyright: ignore[reportInvalidTypeForm]
+    total: int
+    cursor: dict[str, int | float | str] | None = None
+    cursor_string: str | None = None