feat: add support for accessor arrays and refactor stats/base/meankbn2

[gururaj1512]

Resolves #5648

Description

What is the purpose of this pull request?

This pull request:

• update stats/base/meankbn2 to follow latest project conventions
• add support for accessor arrays

Related Issues

Does this pull request have any related issues?

No.

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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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/meankbn2	$\color{green}206/206$ $\color{green}+100.00\%$	$\color{green}8/8$ $\color{green}+100.00\%$	$\color{green}2/2$ $\color{green}+100.00\%$	$\color{green}206/206$ $\color{green}+100.00\%$

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

[kgryte]

LGTM