Summary

• Promote opt-in Level Zero Sysman to a per-field primary Intel GPU metrics source when fresh, with sysfs/WMI fallback retained.
• Add optional Sysman FFI/loading/refresh support for temperature, memory, frequency, fan, plus fresh/seeded diagnostics for engine and power deltas.
• Add per-field source details, Linux hwmon fan priority, Windows Sysman overrides, and docs for the default-off feature gate.

Validation

• cargo fmt --check
• cargo test --lib device::readers::intel_gpu_level_zero --features level_zero
• cargo test --lib device::readers::intel_gpu_linux
• cargo test --lib device::readers::intel_gpu_linux --features level_zero
• cargo test --lib device::readers::intel_gpu_sysfs
• cargo test --lib device::readers::intel_gpu_engine
• cargo test --lib device::readers::intel_gpu_fdinfo
• cargo check --lib --tests
• cargo check --lib --tests --features level_zero
• cargo clippy --lib --tests -- -D warnings
• cargo clippy --lib --tests --features level_zero -- -D warnings
• cargo clippy -- -D warnings
• cargo clippy --features level_zero -- -D warnings
• cargo build --no-default-features --lib
• cargo build --bin all-smi
• cargo build --bin all-smi --features level_zero
• default binary audit: strings target/debug/all-smi | rg 'zeInit|zes(Device|Engine|Power|Temperature|Memory|Frequency|Fan)|libze_loader|ze_loader\.dll' returned no matches
• default binary dynamic dependency audit: ldd target/debug/all-smi contained no libze_loader

Closes #252