Tracking Issue: Implementing a column-based memtable

[tanruixiang]

Describe This Problem

Implementing a column-based memtable

We'll be developing in the impl-column-based-memtable branch, which will eventually merge into the main branch using cherry-pick.

Proposal

Implementing a column-based memtable

Additional Context

• [ ] Designing a columnar memtable approach(There's already a first draft) @tanruixiang
• [ ] https://github.com/CeresDB/ceresdb/issues/1094 @chunshao90
• [ ] https://github.com/CeresDB/ceresdb/issues/1095 @tanruixiang
• [ ] https://github.com/CeresDB/ceresdb/issues/1096 @chunshao90 @tanruixiang
• [ ] Optimize performance in high concurrency read/write scenarios @tanruixiang