[cp-v7.5.6] scheduler: add batch and fix the recovery time of slow store

[okJiang]

What problem does this PR solve?

Issue Number: Ref #9866

What is changed and how does it work?

cherry-pick #8888 and #9388

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]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, rleungx

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• OWNERS [lhy1024,rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-10-29 02:00:10.689913583 +0000 UTC m=+1441916.767166143: ☑️ agreed by rleungx.
• 2025-10-30 02:53:39.626358729 +0000 UTC m=+1531525.703611279: ☑️ agreed by lhy1024.