Server.forever doesn't work with async variables

[Synthetica9]

Description

Server.forever doesn't work with async SharedPVs, probably due to this sleep:

https://github.com/mdavidsaver/p4p/blob/f5c96bad937fff57f5243f72b7fdb89a408d0f4a/src/p4p/server/__init__.py#L175

To reproduce:

Run the following server:

import time
from p4p.nt import NTScalar
from p4p.server import Server
from p4p.server.asyncio import SharedPV

pv = SharedPV(nt=NTScalar('d'), initial=0.0)

@pv.put
async def handle(pv, op):
    pv.post(op.value())
    op.done()

Server.forever(providers=[{'foo': pv}])

Then run pvput foo 12

Observed behaviour

pvput times out:

$ pvput foo 12
Old : 2024-01-15 04:27:05.880  0 
Put timeout

Expected behaviour

pvput succeeds and updates the value

[mdavidsaver]

Indeed Server.forever() is not async, and is in p4p.server instead of p4p.server.asyncio.

In the short term you could instead do something like:

done = asyncio.Event()
# install signal handler to call done.set()
with Server(...):
    await done.wait()

In the longer term, I see the convenience of an async equivalent of Server.forever(). I am not immediately sure where to add it. async/await can't appear in src/p4p/server/__init__.py as long as py2.7 is supported. I am not sure it would be worthwhile to add p4p.server.asyncio.Server just to add one classmethod. Maybe a helper method p4p.server.asyncio.serve_forever()?