feat: Implement write and fork for the new memtable

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR implements write() for the merge tree memtable and adds tests for it.

• write_with_key() and test for the ShardBuilder
• write_with_pk_id() and test for the Shard
• write_with_key() for the Partition.

It also implements most methods for the Partition, Shard, and ShardBuilder except those related to scanning the tree.

• freeze()
• is_empty()
• fork()

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

• Tracking issue for the memtable improvement #2804

[codecov]

Codecov Report

Attention: Patch coverage is 79.22912% with 97 lines in your changes are missing coverage. Please review.

Project coverage is 85.14%. Comparing base (90e9b69) to head (ffa5354).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3357      +/-   ##
==========================================
- Coverage   85.39%   85.14%   -0.26%     
==========================================
  Files         892      892              
  Lines      146042   146412     +370     
==========================================
- Hits       124712   124661      -51     
- Misses      21330    21751     +421     

[fengjiachun]

@evenyag There are some conflicts

[v0y4g3r]

LGTM