Fix is_prime: add proper type hints

Author: AElnamaki

ciphers/sha256.py

@@ -232,7 +232,7 @@ def is_prime(num_to_test: int) -> bool:
     return all(num_to_test % f != 0 for f in range(2, math.isqrt(num_to_test) + 1))
 
 
-def first_n_primes(count_primes: int):
+def first_n_primes(count_primes: int) -> list[int]:
     """
     Generates the first n prime numbers using itertools.count and a primality test.
         Examples: