seq: use faster processing for integer steps from 2 to 200

seq: use faster processing for integer steps from 2 to 200

* src/seq.c: (seq_fast): Accept STEP as a parameter and use that
to skip the output of generated numbers.
(main): Relax to using seq_fast for integer steps between 1 and 200.
For larger steps the throughput was faster using the standard
incrementing procedure.
(cmp): Use the equivalent but faster memcmp for equal len strings.
* tests/misc/seq.pl: Update fast path cases.
Addresses https://bugs.gnu.org/37241