feat(stats/base/dists/f/pdf): add native C addon for evaluating the PDF

[rautelaKamal]

Resolves #{{TODO: add issue number or delete line if NA}}

Description

What is the purpose of this pull request?

This pull request:

• Implements a native C-port for the F Distribution Probability Density Function (@stdlib/stats/base/dists/f/pdf).
• Configures include.gypi, binding.gyp, and manifest.json dependencies via internal N-API mechanisms (STDLIB_MATH_BASE_NAPI_MODULE_DDD_D).
• Validates identical sub-epsilon behavior to pure JS implementation across boundaries, limits, and NaN.
• Introduces robust Boost and Julia test.native.js fixtures to validate the C-port accuracy and benchmarks it.

Related Issues

Does this pull request have any related issues?

This pull request has 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.

This is a Proof of Concept submission towards my GSoC 2026 application regarding porting distributions and specific math functions to high-performance C native addons.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

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• Yes
• No

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

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/f/pdf	$\color{red}596/647$ $\color{green}+92.12%$	$\color{red}61/65$ $\color{green}+93.85%$	$\color{red}5/6$ $\color{green}+83.33%$	$\color{red}596/647$ $\color{green}+92.12%$

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

[rautelaKamal]

Just a quick heads up regarding the minor coverage drop flagged by Codecov:

The native.js file is showing 0% function coverage because the addon.node binary correctly skips compilation during the CI coverage step, which triggers the expected opts.skip = true fallback inside test.native.js. The math logic is fully tested and verified when the native addon actually builds!

Also, the drop in ibeta_power_terms.js relates to the original pure JavaScript implementations and was untouched in this PR. @Planeshifter