This is a follow-up pr to make some changes suggested after approval

[oleksandr-pavlyk]

1. Simplify computation of next n_witems in the power-of-2 branch
2. Add comments explaining hard-coded constants

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[github-actions]

Array API standard conformance tests for dpctl=0.19.0dev0=py310h93fe807_333 ran successfully.
Passed: 894
Failed: 2
Skipped: 118

[coveralls]

coverage: 87.659%. remained the same
when pulling 052a7db on follow-up-to-gh-1932
into 5352dd5 on master.