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/negative-binomial/* packages.
• Replaces uniform() from @stdlib/random/array/uniform for cleaner and more consistent code.
• Moves the random number generation outside the benchmarking loops.
• Updates the test messages to follow code conventions.

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

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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
stats/base/dists/negative-binomial/cdf	$\color{green}272/272$ $\color{green}+0.00%$	$\color{green}29/29$ $\color{green}+0.00%$	$\color{green}3/3$ $\color{green}+0.00%$	$\color{green}272/272$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/kurtosis	$\color{green}193/193$ $\color{green}+0.00%$	$\color{green}11/11$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}193/193$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/logpmf	$\color{red}523/566$ $\color{green}+0.00%$	$\color{red}45/51$ $\color{green}+0.00%$	$\color{green}5/5$ $\color{green}+0.00%$	$\color{red}523/566$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/mean	$\color{green}197/197$ $\color{green}+0.00%$	$\color{green}12/12$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}197/197$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/mode	$\color{green}194/194$ $\color{green}+0.00%$	$\color{green}11/11$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}194/194$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/pmf	$\color{red}532/562$ $\color{green}+0.00%$	$\color{red}49/57$ $\color{green}+0.00%$	$\color{green}5/5$ $\color{green}+0.00%$	$\color{red}532/562$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/quantile	$\color{green}402/402$ $\color{green}+0.00%$	$\color{green}52/52$ $\color{green}+0.00%$	$\color{green}5/5$ $\color{green}+0.00%$	$\color{green}402/402$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/skewness	$\color{green}194/194$ $\color{green}+0.00%$	$\color{green}11/11$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}194/194$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/stdev	$\color{green}194/194$ $\color{green}+0.00%$	$\color{green}11/11$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}194/194$ $\color{green}+0.00%$
stats/base/dists/negative-binomial/variance	$\color{green}189/189$ $\color{green}+0.00%$	$\color{green}11/11$ $\color{green}+0.00%$	$\color{green}2/2$ $\color{green}+0.00%$	$\color{green}189/189$ $\color{green}+0.00%$

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