feat: add C implementation for stats/base/dists/chisquare/pdf

[rautelaKamal]

Description

What is the purpose of this pull request?

This pull request:

• adds a native C implementation for the chi-squared distribution probability density function

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• Refer to [RFC]: Add C implementations to Binomial distribution functions (tracking issue) #3464

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.

The chi-squared PDF is a special case of the gamma PDF. This implementation delegates to the existing C implementation of gamma/pdf.

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

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/chisquare/pdf	$\color{green}219/219$ $\color{green}+0.00%$	$\color{green}7/7$ $\color{green}+0.00%$	$\color{green}3/3$ $\color{green}+0.00%$	$\color{green}219/219$ $\color{green}+0.00%$

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

[Lokeshranjan8]

@rautelaKamal README.md file is missing