pub fn init_parallelism()Expand description
Initialize faer’s global parallelism backend to a Rayon pool sized at
rayon::current_num_threads(). Rayon’s pool itself honors the standard
RAYON_NUM_THREADS environment variable on first use, so callers that
need to constrain the worker count (e.g. the benchmark harnesses) set it
once on the spawned subprocess and rayon picks it up natively.
Idempotent: only the first call has effect (guarded by std::sync::Once).
Without this, faer’s global default is Par::Seq and matmul/factorizations
run single-threaded even when the host has many cores.