Returns a comma-separated number for the given integer.

def friendly_number(self, value: int) -> str:
        """Returns a comma-separated number for the given integer."""
        if self.code not in ("en", "en_US"):
            return str(value)
        s = str(value)
        parts = []
        while s:
            parts.append(s[-3:])
            s = s[:-3]
        return ",".join(reversed(parts))