[ndgrigorian]

This PR improves the implementation of top_k in libtensor by adding several kernels that use a radix select approach, instead of a merge sort approach

There are variants to the kernels:

• Multiple rows processed per work group (best with short rows)
• One row per work-group
• Multiple work-groups per row

Local benchmarking shows a significant performance improvement (results TBA)

Also factors a number of radix-based utilities into a separate header file, which can be reused for future implementations such as median and partition functions

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• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
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• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/3079/index.html

[coveralls]

coverage: 78.606% (-0.003%) from 78.609% — feature/implement-radix-select-topk into master

[github-actions]

Array API standard conformance tests for dpnp=0.21.0dev16=np2py314h8d9cdd5_10 ran successfully.
Passed: 1491
Failed: 0
Skipped: 6