Backport #26122 by @Zettat123
This PR
- Fix #26093. Replace `time.Time` with `timeutil.TimeStamp`
- Fix #26135. Add missing `xorm:"extends"` to `CountLFSMetaObject` for
LFS meta object query
- Add a unit test for LFS meta object garbage collection
Co-authored-by: Zettat123 <zettat123@gmail.com>