* fix: support natural ordering for numbers with >12 digits
Changes the column ordering code when `view_options.natural_order`
is enabled, so that it can support larger numbers.
The previous 12-digit padding approach breaks for numbers above 12
digits.
This length-prefixed approach can scale to much higher numbers.
I picked %03 (padding 3 digits) because most filesystems don't allow
more than 255 bytes in a path segment, and "255" is 3 digits long.
* add memoization to natural order sorting
* remove call to unpack
07f80ad645