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

[headlessNode]

Resolves none.

Description

What is the purpose of this pull request?

This pull request:

• Adds C ndarray API and refactor/cleanup blas/ext/base/dnannsumpw

Related Issues

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No.

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• [x] Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[headlessNode]

@kgryte Same CI error here as the dnansumors package. This appeared after I made the last change. Before it, this CI failure was not present.

[kgryte]

/stdlib merge

[kgryte]

@headlessNode Based on other similar PRs, I believe this PR needs some updates, correct?

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/base/dnannsumpw	$\color{green}611/611$ $\color{green}+100.00\%$	$\color{green}39/39$ $\color{green}+100.00\%$	$\color{green}5/5$ $\color{green}+100.00\%$	$\color{green}611/611$ $\color{green}+100.00\%$

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

[headlessNode]

@kgryte ready for review.