[cherry-pick](branch-2.1) Don't prematurely erase DeleteRows in reading iceberg table with position delete (#47977)

[suxiaogang223]

What problem does this PR solve?

Issue Number: close #41460
Problem Summary:
When reading the Iceberg table, previously read DeleteRows should not be released immediately, as the Iceberg data file is split into multiple IcebergSplits for execution. These IcebergSplits belong to the same data file, meaning they share the same DeleteRows. Therefore, DeleteRows in the DeleteFile should not be released prematurely. Instead, they should be released when the shared_kv is reset, at which point all DeleteRows will be freed along with the cached DeleteFile.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
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4. Which code was refactored and why was this part of the code refactored?
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[suxiaogang223]

run buildall

[doris-robot]

TeamCity be ut coverage result:
Function Coverage: 36.50% (9609/26328)
Line Coverage: 28.09% (79679/283614)
Region Coverage: 26.75% (40866/152790)
Branch Coverage: 23.50% (20712/88144)
Coverage Report: http://coverage.selectdb-in.cc/coverage/b15a10f66c1214ee586f6287ef5b968170ae3e48_b15a10f66c1214ee586f6287ef5b968170ae3e48/report/index.html
Increment Report: http://coverage.selectdb-in.cc/coverage/b15a10f66c1214ee586f6287ef5b968170ae3e48_b15a10f66c1214ee586f6287ef5b968170ae3e48/increment_report/index.html