replace legacy impl with Poll

[loongs-zhang]

No description provided.

[ihciah]

Thank you very much! Please allow me some time to review it!

[ihciah]

Could you re-push it and trigger the CI?
CI was broken before because the company org misconfigured the Action.

[loongs-zhang]

You can also saw CI results in https://github.com/loongs-zhang/monoio/commits/dev-refactor-poll

[loongs-zhang]

I think the CI fails due to cross.

[ihciah]

It's a good change which I wanted long time before(#269).
The only thing I concern is the legacy feature. I think it cannot be treated as poll-io, which is a supplement to polling ability under iouring.

[ihciah]

And another unrelated issue I think about when reading my old PR draft, the latest monoio-macro's test macro seems not work in user code due to some #cfg you introduced 13 months ago. They are not published so the problem haven't affected users. For this issue, I can think about these cases:

1. #[monoio::test] in user code: use iouring by default
2. #[monoio::test(driver=legacy)] in user code: use legacy driver
3. #[monoio::test_all] in user code: generate tests for both drivers
4. #[monoio::test_all] in monoio code: generate tests for both drivers with cfg.

Maybe we can come about a way to fix and do it in another PR.