apps: cover the prime -generate option in the test recipe

Add tests generating a prime in decimal and hex output, verifying the
result is reported prime by feeding it back for primality checking,
checking the -safe option produces p with (p-1)/2 also prime, and
covering the error cases of a missing -bits and a trailing number
argument.

Assisted-by: Claude:claude-fable-5
Reviewed-by: Daniel Kubec <kubec@openssl.foundation>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Merge-date: Mon Sep  7 14:12:35 2026
Merged-from: https://github.com/openssl/openssl/pull/32580