refactor: make write method object safe in WalManager

[ygf11]

Which issue does this PR close?

Part of #72

Rationale for this change

Make WalManager object safe, so we can use Arc in other place.

What changes are included in this PR?

1. Remove LogWriter, and move write to WalManager.
2. Remove generic and associate params in Payload.

Are there any user-facing changes?

No

How does this change test

The refactor is tested by the compiler.

[ygf11]

@waynexia PTAL.

[waynexia]

Fancinating! I plan to review this later this day 🤩

[waynexia]

Thanks for submitting this PR. It looks good to me 👍

For overhead introduced here (Payload becomes a trait object) we can find some way to alleviate it like changing the write interface to directly accept encoded bytes. But this is beyond the scope of the refactor this time. And we are lacking of benchmark so don't know how much regression is brought actually.

I'm going to merge tomorrow if there is no other review.

[ygf11]

Thanks for your suggestions.

For overhead introduced here (Payload becomes a trait object) we can find some way to alleviate it like changing the write interface to directly accept encoded bytes.

I feel the same. we can decouple encoding from write of WalManager. I plan to create a issue about this later, we can talk deeply there :D

But this is beyond the scope of the refactor this time. And we are lacking of benchmark so don't know how much regression is brought actually.

Yes, we need a bench.