feat: add keys method to array/fixed-endian-factory

[ahmad-kashkoush]

Resolves #3148.

Description

What is the purpose of this pull request?

This pull request:

• adds support for a keys method to @stdlib/array/fixed-endian-factory.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves [RFC]: add keys method to array/fixed-endian-factory #3148

Questions

Any questions for reviewers of this pull request?

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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Coverage Report

Package	Statements	Branches	Functions	Lines
array/fixed-endian-factory	$\color{red}1218/1469$ $\color{green}+82.91\%$	$\color{red}153/165$ $\color{green}+92.73\%$	$\color{red}26/36$ $\color{green}+72.22\%$	$\color{red}1218/1469$ $\color{green}+82.91\%$

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

[ahmad-kashkoush]

@kgryte I have resolved conflicts, as well as put keys method into its correct order in both readme and main.js, may you give it a review?

[ahmad-kashkoush]

@kgryte @Planeshifter May you give it a review?