Feature Request: Local.set/Local.reset

[rtpg]

I think a lot of usages of asgiref.local.Local looks a lot like with ContextVars:

def do_thing():
   set_local(some_val)
   do_thing_using_local()
   reset_local()

contextvar.ContextVar has a helpful pair of utils for thsis, set and reset:

var = ContextVar('var')

token = var.set('new value')
# do stuff using var
var.reset(token)
# reverse change

I do feel like Local having something like .set(k, v)/.get(k)/.reset(token) makes sense, especially given that there's a ContextVar under all of this stuff already.

def set(k, v): ... # set local attr k to v, return a token that can be used to reset
def get(k): getattr(self, k)  # more for symmetry with set than anything
def reset(token): ... # reset the state of the _entire Local_ to the state before set

Having said all that I haven't thought about this too deeply, and it might not actually be doable in all use cases. In particular this might not actually play well with context switchups that I saw in #534.