Per spec, unspokenPunctuation defaults to false; the value is stored for
round-tripping but does not change recognition behaviour, since Gecko's
recognizer is LLM-based and only infers punctuation that was not spoken.
Spec: https://webaudio.github.io/web-speech-api/#dom-speechrecognition-unspokenpunctuation
WPT: covered by interfaces/speech-api.idl via idlharness.