NPU plugin test /dev

[wangixt]

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**What you do:**
Implement chroot-based isolation for the NPU plugin unit tests to prevent host `/dev` directory corruption.

**How you do it:**
The unit tests previously used mount namespaces, which do not isolate filesystem data operations, leading to modifications of the host `/dev`. This change introduces `setup_chroot_env()` within `npu_plugin_ut.c` to:
1. Create a new mount namespace.
2. Mount a temporary filesystem (tmpfs) as the new root directory.
3. Create essential directories (`/dev`, `/tmp`, `/run`, `/proc`).
4. Mount a separate tmpfs specifically for `/dev` within the chroot.
5. Recreate necessary character device nodes (`/dev/null`, `/dev/zero`, `/dev/full`).
6. Mount `procfs` for `/proc/self/fd/` resolution.
7. Bind-mount the build directory at its original absolute path to allow `gcov` to write coverage data to the host filesystem.
8. Perform a `chroot()` into this isolated tmpfs root and `chdir("/")`.

This ensures that all file system operations during the unit tests occur within a completely isolated environment, preventing any unintended side effects on the host system. Additionally, `npu_plugin_ut_stubs.c` is updated with necessary stubs for `print_on_level`, `log_get_loglevel`, `criu_get_image_dir`, `cr_system`, and `npu_ut_set_img_dirfd` to enable standalone compilation of the unit test binary. The `npu_plugin.c` source code remains unchanged.

  

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