Draft: Do dot product with Kokkos subview

What is the new feature

Replace ugly expanded dot product with std::inner_product using Kokkos subviews.

How is it implemented

Get vector by Kokkos subview, which can be passed in std::inner_product.

The advantage is

1. No lambda functions, no extra wrapper class.
2. Readable code

The disadvantage is

1. Use functions of Kokkos::Experimental (iterators), which might need to be updated with future Kokkos versions.
2. No guarantee of performance.

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• New feature is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)
• Prior to merging, please remove any boilerplate from the MR description, retaining only the Please describe your feature in a couple of words and describe important implementation details of the feature section to maintain

You are not supposed to merge this request by yourself, the maintainers of libiconmath take care of this action!