[Exec)(cache) add element count in LRU cache

[HappenLee]

cherry-pick #41199

[doris-robot]

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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.

• Release note

  None

Check List (For Reviewer who merge this PR)

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

[HappenLee]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"