update BLAS extension routines

[vtavana]

In this PR, the following changes are made in BLAS extension part of the code

• function arguments are updated to pass by reference where appropriate.
• constant argument are explicitly specified using const keyword.
• naming convention for namespaces are modified to align with recent changes in vm extension.

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[antonwolfy]

@vtavana, thank you for improving code quality!