Function parse 

pub fn parse(input: &str, now: &Zoned) -> Result<Zoned, ParseError>

Parse a natural-language date expression into a jiff::Zoned datetime.

• input – the raw expression (e.g. "next friday", "@1735689600", "in 3 days")
• now – reference “now” for relative resolution

Returns the resolved datetime or a ParseError with span-based diagnostics.