> And of course we have bit packing when we need to pack more efficiently than reasonable; bit-packing with *int_fast8_t* allows you to represent "I need this to take exactly 8 bits of memory, whatever it costs compute-wise, because I'm basically filling memory with these."

AFAICT, "int_fast8_t" is generally typedef to "int", and "int_least8_t" is generally typedef to "char", which conflicts with "I need this to take exactly 8 bits of memory, whatever it costs compute-wise, because I'm basically filling memory with these."