pitr: move step iterate backup files into worker pool (#40577)

[ti-chi-bot]

This is an automated cherry-pick of #40577

Signed-off-by: Leavrth jianjun.liao@outlook.com

What problem does this PR solve?

Issue Number: close #40576

Problem Summary:
the pitr error is overwritten by a meaningless error

What is changed and how it works?

move step iterate backup files into worker pool

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

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix the issue that the pitr error is overwritten by a meaningless error.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth
• joccau

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[joccau]

LGTM

[Leavrth]

/merge

[ti-chi-bot]

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

Commit hash: a5b0059

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