test(server): add test coverage for is_strix_apu() sysfs scanning + rename to is_apu()

[jane-alesi]

Problem

The new SystemInfo::is_strix_apu() function scans /sys/class/kfd/kfd/topology/nodes/*/properties for gfx_target_version, then calls has_unified_memory() on each node. Currently this has no test coverage in test/cpp/test_amd_vram.cpp.

Additionally, the method is hardcoded to "Strix" APUs only. We have an old AMD 2400G APU (Stoney Ridge, gfx v8) that we want to validate detection against -- which means the function name and scope need broadening.

Proposed Solution

1. Rename SystemInfo::is_strix_apu() --> SystemInfo::is_apu() -- broader name reflecting that it detects any AMD APU with unified memory, not just Strix-generation parts.
2. Add sysfs scanning test -- mock or parameterize the KFD path so the test can verify:
   • Correct parsing of gfx_target_version from properties file
   • Multiple node iteration (at least one matching --> return true)
   • Missing/empty nodes gracefully handled
3. Validate on 2400G hardware -- once detection logic covers Stoney Ridge, test against the actual APU.

Related

Depends on future-proof detection logic issue for the detection predicate itself. This issue focuses on renaming + test coverage.

Files to update

• src/cpp/include/lemon/system_info.h -- rename declaration
• src/cpp/server/system_info.cpp -- rename implementation, any callers
• test/cpp/test_amd_vram.cpp -- add test cases
• CMakeLists.txt -- if test dependencies change