stdlib: Fix maximum # of digits for 32-bit integers

[wheremyfoodat]

The maximum 32-bit integer is:

• 2,147,483,647 (for signed integers)
• 4,294,967,295 (for unsigned integers)

In both cases, the number is obviously 10 digits instead of 9. This error would randomly cause memory corruptions when running the rand_gen.pcl program, which prints large numbers given the .input file in this repo.

In my case, the memory corruption would cause a segfault on MacOS, despite going unnoticed on Linux

[wheremyfoodat]

@MarlenaPanagiotakou brought to my attention that the 64-bit case is also wrong (64-bit integers require up to 19 digits for signed integers, or 20 digits for unsigned integers, not 18). In which case, I'd recommend just allocating 20 bytes in case there's ever a language with unsigned integers in this class.

[kostis]

Thanks @wheremyfoodat @MarlenaPanagiotakou for finding and fixing this problem. Merging.