Update randint_untyped to reuse randint implementation

[vlad-perevezentsev]

This PR updates the randint_untyped implementation to reuse randint, adding

• support for array_like (broadcastable) low/high bounds
• support for bounds outside the C long range, which used to raise OverflowError for e.g. randint_untyped(0, 2**40) on Windows
• shared validation so bad bounds report the same errors as randint

The generated values and the int32/int64 result type selection are unchanged.

It also removes irk_discrete_uniform_vec and irk_discrete_uniform_long_vec, left without callers by the change above.

[ndgrigorian]

For the changes only in this PR, this LGTM