feat: add C implementation for blas/ext/base/ndarray/ztril

[yb175]

Related to #14819.

Description

What is the purpose of this pull request?

This pull request:

• Adds a native C ndarray implementation for blas/ext/base/ndarray/ztril, using the existing strided C routine.
• Adds the Node.js addon and uses the native implementation when available, with the JavaScript implementation as a fallback.
• Adds native tests, benchmarks, a C example, and C API documentation.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: add C implementations for blas/ext/base/ndarray packages #14819

Questions

Any questions for reviewers of this pull request?

The native JS wrapper extracts k from the generic scalar ndarray and passes a float64 scalar ndarray to C, so the existing JS example works. For direct C callers, should stdlib_blas_ext_ztril require a 0-D float64 ndarray for k, or support other numeric dtypes? Since the C function returns void, how would you prefer it to handle an unsupported dtype or unreadable scalar?

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

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.".

I used codex for tests generation and documentation writing , all the changes made by ai are reviewed carefully

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Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/base/ndarray/ztril	$\\color{green}231/231$ $\\color{green}+0.00\\%$	$\\color{green}7/7$ $\\color{green}+0.00\\%$	$\\color{green}2/2$ $\\color{green}+0.00\\%$	$\\color{green}231/231$ $\\color{green}+0.00\\%$

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