Improve testing and try to fix MySQL hanging (#32515)

Improve testing and try to fix MySQL hanging (#32515)

By some CI fine tunes (`run tests`), SQLite & MSSQL could complete
in about 12~13 minutes (before > 14), MySQL could complete in 18 minutes
(before: about 23 or even > 30)

Major changes:

1. use tmpfs for MySQL storage
1. run `make test-mysql` instead of `make integration-test-coverage`
because the code coverage is not really used at the moment.
1. refactor testlogger to make it more reliable and be able to report
stuck stacktrace
1. do not requeue failed items when a queue is being flushed (failed
items would keep failing and make flush uncompleted)
1. reduce the file sizes for testing
1. use math ChaCha20 random data instead of crypot/rand (for testing
purpose only)
1. no need to `DeleteRepository` in `TestLinguist`
1. other related refactoring to make code easier to maintain