data_validator: initialize the metrics in Start() instead of constructor

[kennytm]

What problem does this PR solve?

Issue Number: close #12601

What is changed and how it works?

Move the metrics initialization to Start() (which calls initialize()) rather than in the constructor which is called only once in the entire lifetime.

Check List

Tests

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

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Metrics of a restarted DM validator are no longer hidden.

[ti-chi-bot]

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[gemini-code-assist]

Code Review

This pull request moves the initialization of vmetric from the NewContinuousDataValidator constructor to the initialize method in data_validator.go. Additionally, it updates the unit tests in data_validator_test.go to verify that vmetric is correctly initialized upon starting the validator and is re-initialized when the validator is restarted. I have no feedback to provide as there were no review comments.

[kennytm]

/retest

[ti-chi-bot]

@kennytm: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-dm-integration-test-next-gen	ec1f18b	link	false	/test pull-dm-integration-test-next-gen

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[kennytm]

/retest-required

[kennytm]

/cc @GMHDBJD @OliverS929