fix(master): Fix negative storage size metrics after removeAll

[maobaolong]

I0512 23:15:16.652259  1527 allocator.cpp:16] buf_handle_deallocated segment_name=192.168.100.219:12986 size=11
I0512 23:15:16.652276  1527 master_service.cpp:339] action=remove_all_objects, removed_count=1, total_freed_size=11
I0512 23:15:16.652279  1527 scoped_vlog_timer.h:77] RemoveAll response: {"removed_count":1}, latency=64us

I0512 23:15:26.011116  1521 rpc_service.h:78] Master Metrics: Storage: -11.00 B / 75.02 GB (-0.0%) | Keys: 0 | Requests (Success/Total): Put=2/2, Get=0/0, Exist=0/0, Del=0/0, DelAll=1/1

How to test

• start master

/usr/local/lib/python3.12/dist-packages/mooncake/mooncake_master -max_threads 64 -v=1 -metrics_port=8081

• start mooncake-store-service

python3 /usr/local/lib/python3.12/dist-packages/mooncake/mooncake_store_service.py --config=./mooncake.json

• start test

curl -X PUT -H "Content-Type: application/json" -d '{"key":"test1", "value":"sample data"}' http://localhost:8088/api/put
curl -X DELETE http://localhost:8080/api/remove_all