Improve KVStore tests

[CalvinNeo]

What problem does this PR solve?

Issue Number: ref #7256

Problem Summary:

1. fix unstable snapshot tests.
2. improve read index tests.
3. introduce new util functions.
4. old snapshot test don't handle real data. fixed in new snapshot test. However, we will add asserts to show that.
5. move lock parsing codes into a seperated cpp file, will later investigate whether to use ffi to replace it.
6. rename some functions with extra copy. some of those calls should be reimpled to reduce copy.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Lloyd-Pottiger
• hongyunyan

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[CalvinNeo]

/run-all-tests

[CalvinNeo]

/run-all-tests

[CalvinNeo]

/run-all-tests

[CalvinNeo]

/run-all-tests

[Lloyd-Pottiger]

Others LGTM

[CalvinNeo]

/run-all-tests

[hongyunyan]

LGTM

[CalvinNeo]

/run-all-tests

[CalvinNeo]

/run-all-tests

[CalvinNeo]

/merge

[ti-chi-bot]

@CalvinNeo: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: cbaf0bb