Extract string from lines array using Vala string range syntax.
| start_line |
Starting line number (1-indexed, or -1 for invalid/no content) |
| end_line |
Ending line number (1-indexed, exclusive, or -1 for invalid/no content) |
| max_lines |
Maximum number of lines to return (0 or negative = no truncation) |
|
Code snippet or documentation text (empty string if invalid range, truncated if max_lines > 0) |