fix: correct docstrings in prime_numbers.py (list -> generator, grammar fix)

[23f2000188]

Description

The docstrings for slow_primes(), primes(), and fast_primes() in maths/prime_numbers.py incorrectly stated:

"Return a list of all primes numbers up to max."

There are two issues:

1. Incorrect return type description: All three functions are annotated as -> Generator[int] and yield values — they return a generator, not a list.
2. Grammar error: "primes numbers" should be "prime numbers".

Fix

Changed all three occurrences from:

Return a list of all primes numbers up to max.

to:

Return a generator of all prime numbers up to max_n.

Checklist

• The fix is in documentation/docstrings only
• No logic changes
• Consistent with the actual return type annotation Generator[int]
• Grammar corrected