scheduler: refine the interval of scheduling tick in evict-slow-trend-scheduler.

[LykxSassinator]

What problem does this PR solve?

Issue Number: Ref #7156

What is changed and how does it work?

Implement the `GetNextInterval` for `evict-slow-trend-scheduler`, to refine the ticking interval.

Default `GetNextInterval` is not appropriate for `evict-slow-trend-scheduler`, as it might delay
the checking of other nodes' slowness status.

This pr adjusts the ticking interval of the evict-slow-trend-scheduler to optimize
its behavior. If a slow node is already identified as a candidate, the next
interval is now set to be shorter, ensuring quicker subsequent scheduling. 
This refinement aims to decrease response time.

Check List

Tests

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

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• bufferflies
• rleungx

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[codecov]

Codecov Report

Merging #7326 (66b32c8) into master (f1cee6c) will decrease coverage by 0.05%.
The diff coverage is 62.50%.

❗ Current head 66b32c8 differs from pull request most recent head 5f8c2ce. Consider uploading reports for the commit 5f8c2ce to get more accurate results

@@            Coverage Diff             @@
##           master    #7326      +/-   ##
==========================================
- Coverage   74.48%   74.44%   -0.05%     
==========================================
  Files         446      446              
  Lines       48451    48448       -3     
==========================================
- Hits        36090    36066      -24     
- Misses       9174     9189      +15     
- Partials     3187     3193       +6     

Flag	Coverage Δ
unittests	74.44% <62.50%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[LykxSassinator]

/cc @bufferflies

[rleungx]

/merge

[ti-chi-bot]

@rleungx: 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: 66b32c8

[ti-chi-bot]

@LykxSassinator: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.