[BugFix] Fix bRPC stub cache clean timer leak (backport #75973)

[mergify]

Why I'm doing:

there is mem leak caused by bRPC stub cache clean timer leak due to timer is unscheduled but not removed from mem.

std::shared_ptr<PInternalService_RecoverableStub> BrpcStubCache::get_stub(const butil::EndPoint& endpoint) {
    ...
    if (_timer->unschedule((*stub_pool)->_cleanup_task.get()) != TIMER_TASK_RUNNING) {
        timespec tm = butil::seconds_from_now(config::brpc_stub_expire_s);
        auto status = _timer->schedule((*stub_pool)->_cleanup_task.get(), tm);
        if (!status.ok()) {
            LOG(WARNING) << "Failed to schedule brpc cleanup task: " << endpoint;
        }
    }
}

every get_stub() will do _timer->unschedule() and _timer->schedule().
unlike what we expect, _timer->unschedule() will not remove internal objects, thus leak happens

What I'm doing:

extend timer deadline if the stub is still in use instead of unschedule()

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• 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:

• 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 pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5

---

This is an automatic backport of pull request #75973 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 2bbca67 has failed:

On branch mergify/bp/branch-4.0/pr-75973
Your branch is up to date with 'origin/branch-4.0'.

You are currently cherry-picking commit 2bbca67281.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   be/src/util/brpc_stub_cache.cpp
	both modified:   be/src/util/brpc_stub_cache.h
	both modified:   be/test/util/brpc_stub_cache_test.cpp

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr