bench: update random value generation

[hrshya]

Resolves none .

Description

What is the purpose of this pull request?

This pull request:

• Refactors random number generation in JS benchmarks for the stats/base/dists/wald/* packages.
• Moves the random number generation outside the benchmarking loops.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves no related issues.

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
stats/base/dists/wald/mean	$\color{green}184/184$ $\color{green}+100.00%$	$\color{green}10/10$ $\color{green}+100.00%$	$\color{green}2/2$ $\color{green}+100.00%$	$\color{green}184/184$ $\color{green}+100.00%$
stats/base/dists/wald/pdf	$\color{green}360/360$ $\color{green}+100.00%$	$\color{green}33/33$ $\color{green}+100.00%$	$\color{green}4/4$ $\color{green}+100.00%$	$\color{green}360/360$ $\color{green}+100.00%$

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