change store from singleton to object

[mag1c-h]

Purpose

Change store from singleton to object.

Modifications

No user-facing changed.

Test

1. All CI passed with new added/existing test.
2. Unit tests:

[root@localhost ucm.nfsstore]# python3 ./ucm/store/test/e2e/nfsstore_embed.py 
[2025-09-28 08:58:01.512313][UC][I] NFSStore-(Debug). [4004,4004][nfsstore.cc:104,ShowConfig]
[2025-09-28 08:58:01.512404][UC][I] Set UC::StorageBackends to ["."]. [4004,4004][nfsstore.cc:105,ShowConfig]
[2025-09-28 08:58:01.512420][UC][I] Set UC::BlockSize to 8994816. [4004,4004][nfsstore.cc:106,ShowConfig]
[2025-09-28 08:58:01.512435][UC][I] Set UC::TransferEnable to true. [4004,4004][nfsstore.cc:107,ShowConfig]
[2025-09-28 08:58:01.512447][UC][I] Set UC::DeviceId to 1. [4004,4004][nfsstore.cc:108,ShowConfig]
[2025-09-28 08:58:01.512459][UC][I] Set UC::StreamNumber to 32. [4004,4004][nfsstore.cc:109,ShowConfig]
[2025-09-28 08:58:01.512470][UC][I] Set UC::IOSize to 147456. [4004,4004][nfsstore.cc:110,ShowConfig]
[2025-09-28 08:58:01.512483][UC][I] Set UC::BufferNumber to 512. [4004,4004][nfsstore.cc:111,ShowConfig]
[2025-09-28 08:58:01.512494][UC][I] Set UC::TimeoutMs to 30000. [4004,4004][nfsstore.cc:112,ShowConfig]
[2025-09-28 08:58:08.805624][UC][I] Task(1,NFS::D2S,15616,2302672896) finished, elapsed=0.268467s, bw=7.988048GB/s. [4004,4122][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:09.226804][UC][I] Task(2,NFS::D2S,15616,2302672896) finished, elapsed=0.338514s, bw=6.335137GB/s. [4004,4119][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:09.632770][UC][I] Task(3,NFS::D2S,15616,2302672896) finished, elapsed=0.323066s, bw=6.638064GB/s. [4004,4080][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:10.025328][UC][I] Task(4,NFS::D2S,15616,2302672896) finished, elapsed=0.309340s, bw=6.932592GB/s. [4004,4107][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:10.401838][UC][I] Task(5,NFS::D2S,15616,2302672896) finished, elapsed=0.293930s, bw=7.296060GB/s. [4004,4122][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:10.793421][UC][I] Task(6,NFS::D2S,15616,2302672896) finished, elapsed=0.308824s, bw=6.944180GB/s. [4004,4098][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:11.164477][UC][I] Task(7,NFS::D2S,15616,2302672896) finished, elapsed=0.286483s, bw=7.485722GB/s. [4004,4137][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:11.553390][UC][I] Task(8,NFS::D2S,15616,2302672896) finished, elapsed=0.306185s, bw=7.004034GB/s. [4004,4131][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:11.954091][UC][I] Task(9,NFS::D2S,15616,2302672896) finished, elapsed=0.317950s, bw=6.744859GB/s. [4004,4128][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:12.315897][UC][I] Task(10,NFS::D2S,15616,2302672896) finished, elapsed=0.278071s, bw=7.712185GB/s. [4004,4101][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:12.701866][UC][I] Task(11,NFS::D2S,15616,2302672896) finished, elapsed=0.302278s, bw=7.094557GB/s. [4004,4149][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:13.114212][UC][I] Task(12,NFS::D2S,15616,2302672896) finished, elapsed=0.328701s, bw=6.524255GB/s. [4004,4110][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:13.476776][UC][I] Task(13,NFS::D2S,15616,2302672896) finished, elapsed=0.275983s, bw=7.770515GB/s. [4004,4104][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:13.877648][UC][I] Task(14,NFS::D2S,15616,2302672896) finished, elapsed=0.318159s, bw=6.740435GB/s. [4004,4149][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:14.231590][UC][I] Task(15,NFS::D2S,15616,2302672896) finished, elapsed=0.269910s, bw=7.945346GB/s. [4004,4092][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:14.597517][UC][I] Task(16,NFS::D2S,15616,2302672896) finished, elapsed=0.282834s, bw=7.582291GB/s. [4004,4149][tsf_task_waiter.h:43,Done]
[root@localhost ucm.nfsstore]# python3 ./ucm/store/test/e2e/nfsstore_fetch.py 
[2025-09-28 08:58:31.331527][UC][I] NFSStore-(Debug). [4411,4411][nfsstore.cc:104,ShowConfig]
[2025-09-28 08:58:31.331593][UC][I] Set UC::StorageBackends to ["."]. [4411,4411][nfsstore.cc:105,ShowConfig]
[2025-09-28 08:58:31.331608][UC][I] Set UC::BlockSize to 8994816. [4411,4411][nfsstore.cc:106,ShowConfig]
[2025-09-28 08:58:31.331620][UC][I] Set UC::TransferEnable to true. [4411,4411][nfsstore.cc:107,ShowConfig]
[2025-09-28 08:58:31.331631][UC][I] Set UC::DeviceId to 1. [4411,4411][nfsstore.cc:108,ShowConfig]
[2025-09-28 08:58:31.331641][UC][I] Set UC::StreamNumber to 32. [4411,4411][nfsstore.cc:109,ShowConfig]
[2025-09-28 08:58:31.331651][UC][I] Set UC::IOSize to 147456. [4411,4411][nfsstore.cc:110,ShowConfig]
[2025-09-28 08:58:31.331661][UC][I] Set UC::BufferNumber to 512. [4411,4411][nfsstore.cc:111,ShowConfig]
[2025-09-28 08:58:31.331672][UC][I] Set UC::TimeoutMs to 30000. [4411,4411][nfsstore.cc:112,ShowConfig]
[2025-09-28 08:58:38.636879][UC][I] Task(1,NFS::S2D,15616,2302672896) finished, elapsed=0.223118s, bw=9.611650GB/s. [4411,4531][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:39.070475][UC][I] Task(2,NFS::S2D,15616,2302672896) finished, elapsed=0.369508s, bw=5.803750GB/s. [4411,4573][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:39.408690][UC][I] Task(3,NFS::S2D,15616,2302672896) finished, elapsed=0.269291s, bw=7.963612GB/s. [4411,4570][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:39.769389][UC][I] Task(4,NFS::S2D,15616,2302672896) finished, elapsed=0.296394s, bw=7.235402GB/s. [4411,4513][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:40.058318][UC][I] Task(5,NFS::S2D,15616,2302672896) finished, elapsed=0.223845s, bw=9.580426GB/s. [4411,4489][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:40.441024][UC][I] Task(6,NFS::S2D,15616,2302672896) finished, elapsed=0.310318s, bw=6.910750GB/s. [4411,4567][tsf_task_waiter.h:43,Done]
[2025-09-28 08:58:40.731431][UC][I] Task(7,NFS::S2D,15616,2302672896) finished, elapsed=0.221924s, bw=9.663350GB/s. [4411,4531][tsf_task_waiter.h:43,Done]