Problem: memiavl snapshot rewrite could rollback state

[yihuang]

Solution:

• wait for async commit to finish to make sure catching up to latest state.

thanks for @yzang2019 's diagnose.

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PR Checklist:

• Have you read the CONTRIBUTING.md?
• Does your PR follow the C4 patch requirements?
• Have you rebased your work on top of the latest master?
• Have you checked your code compiles? (make)
• Have you included tests for any non-trivial functionality?
• Have you checked your code passes the unit tests? (make test)
• Have you checked your code formatting is correct? (go fmt)
• Have you checked your basic code style is fine? (golangci-lint run)
• If you added any dependencies, have you checked they do not contain any known vulnerabilities? (go list -json -m all | nancy sleuth)
• If your changes affect the client infrastructure, have you run the integration test?
• If your changes affect public APIs, does your PR follow the C4 evolution of public contracts?
• If your code changes public APIs, have you incremented the crate version numbers and documented your changes in the CHANGELOG.md?
• If you are contributing for the first time, please read the agreement in CONTRIBUTING.md now and add a comment to this pull request stating that your PR is in accordance with the Developer's Certificate of Origin.

Thank you for your code, it's appreciated! :)

[codecov]

Codecov Report

Merging #1123 (2618dca) into main (496ce7e) will increase coverage by 0.04%.
The diff coverage is 47.05%.

@@            Coverage Diff             @@
##             main    #1123      +/-   ##
==========================================
+ Coverage   46.19%   46.24%   +0.04%     
==========================================
  Files          82       82              
  Lines        7392     7409      +17     
==========================================
+ Hits         3415     3426      +11     
- Misses       3616     3619       +3     
- Partials      361      364       +3     

Files Changed	Coverage Δ
memiavl/db.go	58.54% <47.05%> (+0.18%)	⬆️