truncate method
Truncates the string to the specified length with optional ellipsis.
If the string is shorter than maxLength, returns the original string.
Example:
'Hello World'.truncate(5); // 'Hello...'
'Hi'.truncate(5); // 'Hi'
Implementation
String truncate(int maxLength, {String ellipsis = '...'}) {
assert(maxLength >= 0, 'maxLength must be non-negative');
if (length <= maxLength) return this;
return '${substring(0, maxLength)}$ellipsis';
}