Replaces static mutable references in perf_libs

[brooksprumo]

Problem

New clippy lints when upgrading to rust 1.84.0.

Some are related to creating references to mutable statics. Here's the new lint for perf::perf_libs:

warning: creating a shared reference to mutable static is discouraged
   --> perf/src/perf_libs.rs:187:14
    |
187 |     unsafe { API.as_ref() }
    |              ^^^^^^^^^^^^ shared reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: shared references to mutable statics are dangerous; it's undefined behavior if the static is mutated or if a mutable reference is created for it while the shared reference lives
    = note: `#[warn(static_mut_refs)]` on by default

Summary of Changes

Replace Once with OnceLock for the API, as it is the preferred way to do Once+data.

Partially fixes #4380