feat: adding 'subarray' prototype method in fixed-endian-factory

[DhruvArvindSingh]

Added necessary changes in test ,benchmark and README.md files

Fixes : #3157

This PR adds 'subarray' prototype method in array/fixed-endian-factory.

Updated files(array/fixed-endian-factory):

• README.md
• main.js

Added files(array/fixed-endian-factory):

• benchmark.subarray.length.js
• benchmark.subarray.js
• test.subarray.js

Read, understood, and

• Read, understood, and followed the contributing guidelines.

---

@stdlib-js/reviewers

[DhruvArvindSingh]

Kindly review this PR @kgryte

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
array/fixed-endian-factory	$\color{red}892/1153$ $\color{green}+77.36\%$	$\color{red}74/84$ $\color{green}+88.10\%$	$\color{red}13/24$ $\color{green}+54.17\%$	$\color{red}892/1153$ $\color{green}+77.36\%$

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