FEAT: make it easy to define generator methods in Actor

[liunux4odoo]

What do these changes do?

Generators can not be transferred directly between actors, users must wrap it to a iterator object referencing to the code of xinference ModelActor.
But the wrapping codes are complex and need to rewrite them in every generators.

This PR provides a decorator: xo.generator, users can define generators as usual in a simple way:

import asyncio
import time
import xoscar as xo


address = "127.0.0.1:8000"

class WorkerActor(xo.StatelessActor):
    @xo.generator
    def chat(self):
        for x in "hello oscar by sync":
            yield x
            time.sleep(0.1)

    @xo.generator
    async def achat(self):
        for x in "hello oscar by async":
            yield x
            await asyncio.sleep(0.1)

    @classmethod
    def uid(cls):
        return "worker"


class SupervisorActor(xo.StatelessActor):
    @xo.generator
    async def chat(self):
        worker_actor: xo.ActorRef["WorkerActor"] = await xo.actor_ref(address=address, uid=WorkerActor.uid())
        yield "\nsync"
        async for x in await worker_actor.chat(): # this is much confused. I will suggest use async generators only.
            yield x
        
        yield "\nasync"
        async for x in await worker_actor.achat():
            yield x

    @classmethod
    def uid(cls):
        return "supervisor"


async def main():
    pool = await xo.create_actor_pool(address, 2)
    await xo.create_actor(WorkerActor, address=address, uid=WorkerActor.uid())
    superivsor_actor = await xo.create_actor(SupervisorActor, address=address, uid=SupervisorActor.uid())

    async for x in await superivsor_actor.chat():
        print(x)

    await pool.join()


asyncio.run(main())

Related issue number

Fixes #xxxx

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c7f3de4) 89.02% compared to head (c4d53a2) 88.62%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
- Coverage   89.02%   88.62%   -0.41%     
==========================================
  Files          48       47       -1     
  Lines        4010     3920      -90     
  Branches      764      751      -13     
==========================================
- Hits         3570     3474      -96     
- Misses        355      360       +5     
- Partials       85       86       +1     

Flag	Coverage Δ
unittests	88.54% <ø> (-0.31%)	⬇️

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[codingl2k1]

Known issue: If the caller crashes, the generator will leak.