Cleanly iteratively concatenate a string

[hearty latch]

Will try to convert this to an arraylist for now

fn colorize_line(allocator: Allocator, s: []const u8, match_it: *mvzr.Regex.RegexIterator) ![]const u8 {
    var start: usize = 0;
    var line = try std.ArrayList(u8).initCapacity(allocator, s.len);

    while (match_it.next()) |m| {
        // Color the current match
        const colorized_match = try colorize(allocator, m.slice);
        // Append everything from the end of the last match to the start of the current
        try line.appendSlice(s[start..m.start]);
        // Append the colorized match
        try line.appendSlice(colorized_match);
        allocator.free(colorized_match);
        // Update the cursor to the end of the match
        start = m.end;
    }

    // Append everything after the last match
    try line.appendSlice(s[start..]);
    return line.items;
}

is probably a lot more reasonable