utest: move core utest cases to under src/utest

[unicornx]

将原先 examples/utest/testcases/kernel/ 目录下的单元测试用例移到 src/utest/ 下（src/utest/ 是一个新建的目录）。

同时修改这些测试用例的名字，用 core 代替 src 作为 case name 的 模块前缀，参考 #10698

为方便 review，本 pr 包括两个 commit，merge 时请尽量保留，不要压缩。

• utest: move core tesetcases under to directiry "src"：只是移动文件位置
• utest: core: unify case names：修改 cases 的 name。

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流。
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[github-actions]

📌 Code Review Assignment

🏷️ Tag: kernel

Reviewers: @GorrayLi @ReviewSun @hamburger-os @lianux-mm @wdfk-prog @xu18838022837

Changed Files (Click to expand)

• src/utest/Kconfig
• src/utest/SConscript
• src/utest/atomic_tc.c
• src/utest/device_tc.c
• src/utest/event_tc.c
• src/utest/hooklist_tc.c
• src/utest/irq_tc.c
• src/utest/mailbox_tc.c
• src/utest/mem_tc.c
• src/utest/memheap_tc.c
• src/utest/mempool_tc.c
• src/utest/messagequeue_tc.c
• src/utest/mtsafe_kprint_tc.c
• src/utest/mutex_pi_tc.c
• src/utest/mutex_tc.c
• src/utest/object_tc.c
• src/utest/sched_mtx_tc.c
• src/utest/sched_sem_tc.c
• src/utest/sched_thread_tc.c
• src/utest/sched_timed_mtx_tc.c
• src/utest/sched_timed_sem_tc.c
• src/utest/semaphore_tc.c
• src/utest/signal_tc.c
• src/utest/slab_tc.c
• src/utest/smp/Kconfig
• src/utest/smp/SConscript
• src/utest/smp/smp_affinity_pri1_tc.c
• src/utest/smp/smp_affinity_pri2_tc.c
• src/utest/smp/smp_assigned_idle_cores_tc.c

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📊 Current Review Status (Last Updated: 2025-09-25 15:08 CST)

• ⌛ @GorrayLi Pending Review
• ⌛ @ReviewSun Pending Review
• ⌛ @hamburger-os Pending Review
• ⌛ @lianux-mm Pending Review
• ⌛ @wdfk-prog Pending Review
• ⌛ @xu18838022837 Pending Review

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