Add test cases for sysinfo/

[DingmaomaoBJTU]

[xieofxie]

Tests now exist in tests/unit/sysinfo/:

• test_device.py
• test_helper.py
• test_software.py
• test_sysinfo.py
• conftest.py

Coverage gaps that still warrant the issue staying open:

• No test_hardware.py — CPU, GPU, NPU, RAM classes and get_vendor_id_device_id_from_pnp_id() in hardware.py are untested.
• No test_pdh_adapters.py — enumerate_adapters(), discover_npu_luid(), discover_gpu_luids(), resolve_adapter_luid() in pdh_adapters.py
  are untested.