Function decode 

pub fn decode(input: &[u8]) -> Result<&str, DecodeError<'_>>

Decode a byte slice as UTF-8, returning the valid prefix on error.

Unlike std::str::from_utf8(), this distinguishes between invalid and incomplete byte sequences so that callers can request more input.

use utf8_zero::{decode, DecodeError};

// Fully valid input.
assert_eq!(decode(b"hello").unwrap(), "hello");

// Invalid byte — returns the valid prefix and the bad sequence.
match decode(b"hello\xC0world") {
    Err(DecodeError::Invalid { valid_prefix, .. }) => {
        assert_eq!(valid_prefix, "hello");
    }
    _ => unreachable!(),
}

// Input ends mid-codepoint — returns Incomplete so the caller can
// supply more bytes.
match decode(b"\xC3") {
    Err(DecodeError::Incomplete { valid_prefix, incomplete_suffix }) => {
        assert_eq!(valid_prefix, "");
        assert_eq!(incomplete_suffix.buffer_len, 1);
    }
    _ => unreachable!(),
}