Add context local resource

[elina-israyelyan]

Closes Issue #728 , #760
Relates to #699

Added a ContextLocalResource class that inherits from Resource and overrides it so that the actual _resource and _shutdowner are stored and retrieved via ContextVar.
This allows each context (such as a FastAPI request) to have its own instance of the resource.
Since FastAPI creates a new context per request, each request now gets its own context-scoped resource.
Because the class extends Resource, the Closing marker continues to work as expected.

Demo
Run the following API, then do concurrent requests.

from dependency_injector import containers, providers from dependency_injector.wiring import Closing, Provide, inject from fastapi import Depends, FastAPI from uuid import uuid4 global_list = [] class AsyncSessionLocal: def __init__(self): self.id = uuid4() async def __aenter__(self): print("entering session") return self async def __aexit__(self, exc_type, exc_val, exc_tb): print("closing session") async def execute(self, user_input): return "executing " + user_input async def get_session() -> AsyncSessionLocal: print("start session") async with AsyncSessionLocal() as session: yield session print("close session") app = FastAPI() class Container(containers.DeclarativeContainer): db = providers.ContextLocalResource(get_session) @app.get("/") @inject async def index(db: AsyncSessionLocal = Depends(Closing[Provide["db"]])): global global_list if db.id in global_list: raise Exception("The db session is already being used") # never reaches here global_list.append(db.id) res = await db.execute("SELECT 1") return str(res) if __name__ == "__main__": import uvicorn container = Container() container.wire(modules=["__main__"]) uvicorn.run(app, host="localhost", port=8000) container.unwire()