feat: add C ndarray API and refactor blas/ext/base/dsnansum

[headlessNode]

Description

What is the purpose of this pull request?

This pull request:

• add C ndarray API and refactor/cleanup blas/ext/base/dsnansumpw

Related Issues

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No.

Questions

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No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/base/dsnansum	$\color{green}345/345$ $\color{green}+100.00\%$	$\color{green}13/13$ $\color{green}+100.00\%$	$\color{green}4/4$ $\color{green}+100.00\%$	$\color{green}345/345$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

LGTM. Thanks, @headlessNode!