Function parse_bracket_segment 

pub fn parse_bracket_segment(
    seg: &str,
    default_delimiter: char,
) -> Result<(usize, char)>

Parse the bracket length segment, extracting length and delimiter.

The cap on declared length is enforced by parse_array_header_line after a successful parse so that unrelated [abc] literals inside key-value content still fall through to non-array handling instead of erroring.

Errors

Returns an error if the length is not a valid unsigned integer.