add lifetime hooks

[AdamVerner]

Currently, in one of my codebases, the following code gets repeated in every function.

from admin_table.application import current_user
async def my_function(param1: str, ...) -> None:
    async with async_manager() as mgr:
        mgr.set_security_context(user_id=current_user.user_id)
        mgr.call_private_function()

It would be nice to setup request-lifetime hooks in order to remove the redundant code.
We could, for example, pass request_lifespan (similarily as fastapi does) to the config, which would then wrap every request.
So the afformentioned case would be simplified to the following code

from contextvars import ContextVar
from contextlib import asynccontextmanager

from admin_table.application import current_user

mgr = ContextVar("mgr")

@asynccontextmanager
async def request_lifespan():
    async with async_manager() as scope_mgr:
        scope_mgr.set_security_context(user_id=current_user.user_id)
        token = mgr.set(scope_mgr)
        try:
            yield
        finally:
            mgr.reset(token)
    

async def my_function(param1: str, ...) -> None:
        mgr.get().call_private_function()