fix(profile): gate pstate_name with its caller

`pstate_name` went in at module scope without `#[cfg(feature = "nvidia")]`,
so `nvml_wrapper` was unlinked for every feature set that does not enable
nvidia, and CI's Feature combinations job failed on `7c79f8b`.

The local gate cannot catch this and that is the part worth recording.
`clippy --all-features`, `test --all-features` and *both* cross-target
checks all enable nvidia — the cross-checks name it in their feature lists —
so the whole gate was green on a commit that does not build with
`--no-default-features --features cpu`.

Checked directly this time: no features, cpu, cli, io, network, amd and
intel all build. The note in HANDOFF says which cheap subset approximates
the twenty-feature loop CI runs, and which directories mix vendor-gated code
with ungated code, since that is where the mistake is available to make.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>