Summary:
When intents cleanup finds file to delete it invokes regular db flush.
During shutdown this flush could fail, but failure is not returned to the caller (cleanup procedure in this case).
As result we could get into situation where intents file was removed but regular db was not flushed.
It leads to data loss, since removed file could have intents that was not yet persisted in regular db.

Also:
1) Fixed and improved vector index stats reporting (initial issue was found by vector index test).
2) Fixed issue with tablet server shutdown when wait queue is used. The check was failing that there are active tokens on corresponding thread pool.

Jira: DB-15832

Test Plan: PgTxnTest.CleanupIntentsDuringShutdown

Reviewers: timur

Reviewed By: timur

Subscribers: ybase, yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D42661