[Enhancement][Draft]change update_tablet_meta_info thread pool max thread to 2

[sevev]

Why I'm doing:

What I'm doing:

Fixes #issue

What type of PR is this:

• [ ] BugFix
• [ ] Feature
• [x] Enhancement
• [ ] Refactor
• [ ] UT
• [ ] Doc
• [ ] Tool

Does this PR entail a change in behavior?

• [ ] Yes, this PR will result in a change in behavior.
• [x] No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• [ ] Interface/UI changes: syntax, type conversion, expression evaluation, display information
• [ ] Parameter changes: default values, similar parameters but with different default values
• [ ] Policy changes: use new policy to replace old one, functionality automatically enabled
• [ ] Feature removed
• [ ] Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• [x] I have added test cases for my bug fix or my new feature
• [ ] This pr needs user documentation (for new or modified features or behaviors)
  • [ ] I have added documentation for my new feature or new function
• [ ] This is a backport pr

Bugfix cherry-pick branch check:

• [x] I have checked the version labels which the pr will be auto-backported to the target branch
  • [ ] 4.0
  • [ ] 3.5
  • [ ] 3.4
  • [ ] 3.3

---

[!NOTE] Makes the UPDATE_TABLET_META_INFO thread pool size configurable via update_tablet_meta_info_worker_count and adds start/end timing logs to LakeServiceImpl::get_tablet_stats, plus elevates update-meta task log level to INFO.

• Agent Server:
  • Configure update_tablet_meta_info thread pool using calc_real_num_threads(config::update_tablet_meta_info_worker_count) instead of a fixed size.
• Config:
  • Add config::update_tablet_meta_info_worker_count (default 2, 0 = CPU cores) to control UPDATE_TABLET_META_INFO pool.
• Lake Service:
  • get_tablet_stats adds start/end INFO logs and elapsed timing; minor refactor to cache tablet_count.
• Logging:
  • Promote update tablet meta task start log from verbose to INFO.

^{Written by Cursor Bugbot for commit 1451c6fa5e4d81a49fb67167149f588115448702. This will update automatically on new commits. Configure here.}

[mergify[bot]]

🧪 CI Insights

Here's what we observed from your CI run for 1451c6fa.

🟢 All jobs passed!

But CI Insights is watching 👀

[github-actions[bot]]

[FE Incremental Coverage Report]

:white_check_mark: pass : 0 / 0 (0%)

[github-actions[bot]]

[Java-Extensions Incremental Coverage Report]

:white_check_mark: pass : 0 / 0 (0%)

[github-actions[bot]]

[BE Incremental Coverage Report]

:white_check_mark: pass : 0 / 0 (0%)

[alvin-celerdata]

@cursor review