[fix](file cache) Avoid accessing expired HDFS profile during prefetch

[bobhan1]

What problem does this PR solve?

Issue Number: DORIS-28268

Related PR: None

Problem Summary:

CachedRemoteFileReader::prefetch_range() submits fire-and-forget dry-run tasks. A running task keeps the cached reader and its underlying HdfsFileReader alive, but it does not keep the query RuntimeProfile alive. HdfsFileReader::read_at_impl() previously always updated _total_read_time, so a delayed prefetch read could access that counter after the query profile had been freed.

Skip the query-profile timer for dry-run reads. Normal HDFS reads keep their existing profile accounting, and prefetch/cache-population behavior is unchanged.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
    • ./build.sh --be -j100 is running; the result will be updated after completion.
  • 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. Dry-run HDFS reads no longer update the query HdfsIO timer; data reads and file-cache population are unchanged.

• 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?
5. Which functions were optimized and what is the difference before and after the optimization?

[bobhan1]

run buildall

[hello-stephen]

BE UT Coverage Report

Increment line coverage 0.00% (0/2) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	59.44% (25664/43178)
Line Coverage	43.92% (262338/597307)
Region Coverage	39.87% (207942/521536)
Branch Coverage	41.32% (95810/231879)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 0.00% (0/2) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	74.13% (31187/42071)
Line Coverage	58.32% (345707/592815)
Region Coverage	55.13% (288214/522815)
Branch Coverage	55.95% (129591/231613)

[gavinchou]

seems read_timer may still endup with nullptr?