feat: add constants/float16/sqrt-half-pi

[GlyphicGuy]

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Resolves a part of #9061

Description

What is the purpose of this pull request?

This pull request:

• adds constants/float16/sqrt-half-pi

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: tracking issue for missing float16 constants #9061

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.

I tried to understand and learn from the existing constants in the ../constants/ directory along with the recent PRs as reference to put together this PR. Kindly guide me as this is my first attempt to contribute to this repo and if there is any scope of improvement I'd like to fix those. I did read the guidelines and have tried to follow those carefully to the best of my knowledge at every step, but if there are any problems, please help me through it.
Thank you.

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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• 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-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
constants/float16/sqrt-half-pi	$\color{green}48/48$ $\color{green}+100.00%$	$\color{green}1/1$ $\color{green}+100.00%$	$\color{green}0/0$ $\color{green}+100.00%$	$\color{green}48/48$ $\color{green}+100.00%$

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