Trim surrounding whitespace

strip(), lstrip(), and rstrip() remove Unicode whitespace from both ends, the left end, or the right end. Each returns Result[str, AllocError]:

def main() -> Result[(), AllocError | IoError]:
    text = "  é🙂  "
    print(str.repr(text.strip())?)?
    print(str.repr(text.lstrip())?)?
    print(str.repr(text.rstrip())?)?
    print(str.repr(" \t\n".strip())?)?
    Ok(())

Result[str, AllocError].Ok("é🙂")
Result[str, AllocError].Ok("é🙂  ")
Result[str, AllocError].Ok("  é🙂")
Result[str, AllocError].Ok("")

They borrow the source and allocate only the final independent string. Empty and unchanged results still need that allocation. Interior whitespace is kept; NUL and zero-width space are not trimmed. These methods use Unicode White_Space and take no arguments; custom character sets are not supported yet.