Move snapshot data write to async mode.

[xiaoxichen]

In order to provider higher queue depth for disk, which is optimal for scheduler to merge requests.

Also IO and compute(checksum) can parallel.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 55.10204% with 22 lines in your changes missing coverage. Please review.

Project coverage is 59.73%. Comparing base (1746bcc) to head (9b987c2).
Report is 71 commits behind head on main.

Files with missing lines	Patch %	Lines
...lib/homestore_backend/snapshot_receive_handler.cpp	55.10%	17 Missing and 5 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #299      +/-   ##
==========================================
- Coverage   63.15%   59.73%   -3.42%     
==========================================
  Files          32       33       +1     
  Lines        1900     3055    +1155     
  Branches      204      364     +160     
==========================================
+ Hits         1200     1825     +625     
- Misses        600     1034     +434     
- Partials      100      196      +96     

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[koujl]

Seems should be

std::unique_lock< std::shared_mutex > lock(ctx_->progress_lock);

[yuwmao]

If a blob batch returns an error due to ALLOC_BLK_ERR, the async_write might still be in progress.
Then when the retry batch with the same blobs comes, is there any problem? Seems no correctness issue due to the duplication handling but could have some space waste(the previous write might not be committed in indexservice when second write happens)?