Fix: snapshot lock

[akiradeveloper]

Existence of snapshot and the corresponding snapshot entry should be atomic.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.59%. Comparing base (40c17f7) to head (f63aee7).

Files with missing lines	Patch %	Lines
sorock/src/process/raft_process/responder.rs	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #451      +/-   ##
==========================================
+ Coverage   94.56%   94.59%   +0.02%     
==========================================
  Files          47       47              
  Lines        2448     2441       -7     
==========================================
- Hits         2315     2309       -6     
+ Misses        133      132       -1     

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