bench: refactor random number generation in number/int32/base/mul

[impawstarlight]

Resolves none.

Description

What is the purpose of this pull request?

This pull request:

• Refactors random number generation in JS benchmarks for number/int32/base/mul
• Moves the random number generation outside the benchmarking loops
• Replaces minstd() usage with discreteUniform()
• Replaces isnan() checks with range based checks for integer focused code path

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.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

{{TODO: add disclosure if applicable}}

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
number/int32/base/mul	$\color{green}211/211$ $\color{green}+0.00%$	$\color{red}6/7$ $\color{green}+0.00%$	$\color{green}1/1$ $\color{green}+0.00%$	$\color{green}211/211$ $\color{green}+0.00%$

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

[kgryte]

LGTM. Thanks for cleaning up, @impawstarlight!