Native format decoding and normalization use up to two CPU workers for
batches of at least 256 distinct, normalized inputs. Smaller batches are
decoded serially. Set options(glyparse.threads = 1L) to disable parallel
decoding, or set an integer between 1 and 64 to choose the worker limit.
Each worker has its own residue cache. R object allocation, validation,
progress reporting, and graph construction run on the calling thread.
No complete input or parsed result is cached between calls.