test: Add tests for KvBackend trait implement

[poltao]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

close #2618

What's changed and what's your intention?

For now, KvBackend trait has some implements, such as ChrootKvBackend, MemoryKvBackend, etc. But only RaftEngineBackend, MemoryKvBackend and EtcdStore will directly access the data. PR #2615 has been added some tests for RaftEngineBackend and MemoryKvBackend, this PR for EtcdStore to ensure all implements have the same behaviors.

Other KvBackend trait implements based RaftEngineBackend, MemoryKvBackend and EtcdStore implement，I think it's unnecessary.

Tests mainly for range、put、batch_put、batch_get、compare_and_put、delete_range、batch_delete.

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.

[codecov]

Codecov Report

Attention: Patch coverage is 99.03846% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 85.23%. Comparing base (db329f6) to head (9644cb3).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3700      +/-   ##
==========================================
- Coverage   85.57%   85.23%   -0.34%     
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  Files         962      963       +1     
  Lines      160274   160605     +331     
==========================================
- Hits       137155   136898     -257     
- Misses      23119    23707     +588     

[killme2008]

@realtaobo Thank you. There are some TOML format issues and cargo clippy warnings, could you fix them?

[tisonkun]

@realtaobo Please update the PR description for what behavior tests your added.

Reverse engineering and guess from the code is unfriendly for reviewers.

[poltao]

Reverse engineering and guess from the code is unfriendly for reviewers.

Got it. Finished.

[tisonkun]

cc @MichaelScofield PTAL.