parser apparently aliases the `state` argument to internal functions

OK, inserted `return parseSymbol(state)` at the point where `not` is detected. Note that it's necessary to restore `state` to what it was before grabbing the `(` token; you can't just return `parseSymbol(saveState)`. In other words, the `state` object that comes into parseUnary must be aliased somewhere, so that if it doesn't agree with the state passed into parseSymbol then the parse is spoiled. Should I file an issue about that, or just not worry about it since the parser is working as long as you properly update the input state object in every parseXxx() function? (I'm inclined toward the latter.)

_Originally posted by @gwhitney in https://github.com/josdejong/mathjs/pull/3611#discussion_r2641366557_