feat: add blas/ext/base/sindex-of

[headlessNode]

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type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes. report:

• task: lint_filenames status: passed
• task: lint_editorconfig status: passed
• task: lint_markdown status: passed
• task: lint_package_json status: passed
• task: lint_repl_help status: passed
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• task: lint_c_src status: na
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Progresses #2656 .

Description

What is the purpose of this pull request?

This pull request:

• add blas/ext/base/sindexof

Related Issues

Does this pull request have any related issues?

This pull request:

• Progresses [RFC]: achieve ndarray API parity with built-in JavaScript arrays  #2656

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-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/base/sindex-of	$\color{green}357/357$ $\color{green}+100.00\%$	$\color{green}19/19$ $\color{green}+100.00\%$	$\color{green}4/4$ $\color{green}+100.00\%$	$\color{green}357/357$ $\color{green}+100.00\%$

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

[kgryte]

@headlessNode Would you mind going ahead and adding the C implementation and associated benchmarks, examples, docs, and tests?

[kgryte]

LGTM after a fair amount of clean-up.