feat: Add freeze and fork method to the memtable

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR changes some APIs of the memtable

• Renames mark_immutable() to freeze(). freeze() turns a mutable memtable into an immutable memtable and this operation is fallible.
• Adds a fork() method to create a new mutable memtable from an immutable memtable.
  • It allows the new memtable to reuse some data in the old memtable
• The iter() method is fallible.

Now the region instead of the memtable builder generates the memtable id. So the memtable builder needs to take a memtable id to build a new memtable.

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

[fengjiachun]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 67.94872% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 85.20%. Comparing base (1df64f2) to head (9f64bbe).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3374      +/-   ##
==========================================
- Coverage   85.59%   85.20%   -0.39%     
==========================================
  Files         892      892              
  Lines      146564   146596      +32     
==========================================
- Hits       125448   124912     -536     
- Misses      21116    21684     +568     

[v0y4g3r]

LGTM