Fixed bug on naming individual commands with parameter scan

[teofr]

When using -P together with --command-name there was a bug when trying to instantiate every individual command name of more than one command.

$ hyperfine  "echo {foo}" "sleep {foo}" -P foo 1 3 -n "echo 1" -n "sleep 1" -n "echo 2" -n "sleep 2"

Would error out with:

Error: '--command-name' has been specified 4 times. It has to appear exactly once, or exactly 3 times (number of benchmarks)

Also, stopped using the hint of the iterator since it could become quite problematic if either gives a wrong hint or None.
This whole bit could use a refactor, but this seemed like a low hanging fruit.