init: new structure + fix lint errors

cpv3/db/session.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from collections.abc import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+
+from cpv3.infrastructure.settings import get_settings
+
+
+_settings = get_settings()
+_engine = create_async_engine(
+    _settings.get_database_url(),
+    echo=_settings.debug,
+    pool_pre_ping=True,
+)
+
+SessionLocal = async_sessionmaker(bind=_engine, class_=AsyncSession, expire_on_commit=False)
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    async with SessionLocal() as session:
+        yield session