In order to add common code to the value deleter of LRU cache, let all lru cache values inherit from LRUCacheValueBase class and tracking memory in destructor.
Remove LRUCacheValueBase, put last_visit_time into LRUHandle, and automatically update timestamp to last_visit_time during cache insert and lookup.
Do not rely on external modification of last_visit_time, which is often forgotten.
TabletSchema and Schema no longer track memory, only track columns count. because cannot accurately track memory size.
TabletMeta MemTracker changed to track TabletSchema columns count.
Segment::_meta_mem_usage Unknown value overflow, causes the value of SegmentMeta MemTracker is similar to -2912341218700198079. So, temporarily put it in experimental type tracker.
Current initialization dependency:
Daemon ───┬──► StorageEngine ──► ExecEnv ──► Disk/Mem/CpuInfo
│
│
BackendService ─┘
However, original code incorrectly initialize Daemon before StorageEngine.
This PR also stop and join threads of daemon services in their dtor, to ensure Daemon services release resources in reverse order of initialization via RAII.
