[fix](be) Fix file cache queue evict size metrics (#64897)

[deardeng]

pick from #64897
Problem Summary: File cache queue evict size metrics were constructed with literal array indexes, while increments use FileCacheType enum values. Because FileCacheType maps DISPOSABLE to 0 and INDEX to 2, file_cache_index_queue_evict_size actually counted disposable queue evictions, and file_cache_disposable_queue_evict_size counted index queue evictions. This change initializes the metrics array with explicit FileCacheType indexes so each bvar name matches the queue type that increments it.

(cherry picked from commit 7f0ab56)

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

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.
Don't know what should be done next? See How to process your PR.

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.
3. What features were added. Why was this function added?
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?

[deardeng]

run buildall

[hello-stephen]

BE UT Coverage Report

Increment line coverage 100.00% (7/7) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	53.58% (19594/36568)
Line Coverage	36.64% (183408/500559)
Region Coverage	33.20% (142611/429512)
Branch Coverage	34.06% (61665/181026)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (7/7) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	71.48% (25571/35775)
Line Coverage	54.38% (271286/498905)
Region Coverage	51.97% (224995/432940)
Branch Coverage	53.35% (96800/181448)