refactor: optimize number/int32/base/muldw implementation for better performance

[impawstarlight]

Resolves none.

Description

What is the purpose of this pull request?

This pull request:

• Optimizes number/int32/base/muldw implementation to improve performance by moving the isnan check out of the lower level implementation.
• Utilizes number/int32/base/mul for computing the lower half of the double word product to reduce unnecessary calculation.
• Remove NaN tests for the lower level implementation.

Related Issues

Does this pull request have any related issues?

No.

Questions

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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?

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• No

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• Test/benchmark generation
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{{TODO: add disclosure if applicable}}

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[impawstarlight]

/stdlib update-copyright-years

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Coverage Report

Package	Statements	Branches	Functions	Lines
number/int32/base/muldw	$\color{green}184/184$ $\color{green}+100.00%$	$\color{green}8/8$ $\color{green}+100.00%$	$\color{green}2/2$ $\color{green}+100.00%$	$\color{green}184/184$ $\color{green}+100.00%$

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