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

[pranav-1720]

Resolves #3142

Description

What is the purpose of this pull request?

This pull request:

• Adds findIndex method to array/fixed-endian-factory
• Add tests for the respective method
• Add benchmarks files for the respective method
• Updates README for fixed-endian-factory for the respective method

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves #3142

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

No.

Checklist

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

• Read, understood, and followed the contributing guidelines.

---

@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
array/fixed-endian-factory	$\color{red}920/1179$ $\color{green}+78.03\%$	$\color{red}82/92$ $\color{green}+89.13\%$	$\color{red}16/27$ $\color{green}+59.26\%$	$\color{red}920/1179$ $\color{green}+78.03\%$

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

[pranav-1720]

@Planeshifter Hi, just reviving this as this PR was mostly completed