[WIP]refactor: try to replace dynamic-dispatch with pre-code in wal write

[ygf11]

Which issue does this PR close?

Closes #162

Rationale for this change

Pre-code maybe more elegant and fast than dynamic dispatch.

What changes are included in this PR?

• Using common LogEncoding for rock_impl and table_kv_impl.
• Add WalManager::encoder() to pre-encode payloads.
• Fix tests and benchmark.

Are there any user-facing changes?

No

How does this change test

Unit tests will test it.