docs: fix TSDoc issues in several @stdlib/math/iter declarations

[Planeshifter]

Description

What is the purpose of this pull request?

This pull request corrects documentation-only issues in TypeScript declaration files across the @stdlib/math/iter namespace, flagged by an audit:

• sequences/nonpositive-even-integers — the iter option @throws said "nonpositive integer"; iter is an iteration count, so it must be "nonnegative integer" (matching every sibling sequence package and the package's own lib/validate.js).
• special/ahaversin — "versed sin" → "versed sine" in the summary and Notes.
• tools/map — added the non-numeric/NaN handling Notes bullet that the sibling map2/map3 declarations include.
• special/acoth — spelled out the infinity notation in the domain note ((-infinity,-1], [1,+infinity)) to match the sibling acosh.

This PR addresses only the TypeScript declaration files. Two further iter findings — special/pow ("exponential function" → "power function") and the sequences/integers default value — are package-wide and handled in a separate PR (#12473).

Related Issues

Does this pull request have any related issues?

No.

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request?

Found via a TypeScript-declaration audit of the @stdlib/math namespace.

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.

These issues were identified by an automated TypeScript-declaration audit run with Claude Code, and the fixes were prepared by Claude Code under my review.

---

@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/iter/sequences/nonpositive-even-integers	$\color{green}264/264$ $\color{green}+0.00\%$	$\color{green}22/22$ $\color{green}+0.00\%$	$\color{green}5/5$ $\color{green}+0.00\%$	$\color{green}264/264$ $\color{green}+0.00\%$
math/iter/special/acoth	$\color{green}115/115$ $\color{green}+0.00\%$	$\color{green}3/3$ $\color{green}+0.00\%$	$\color{green}1/1$ $\color{green}+0.00\%$	$\color{green}115/115$ $\color{green}+0.00\%$
math/iter/special/ahaversin	$\color{green}115/115$ $\color{green}+0.00\%$	$\color{green}3/3$ $\color{green}+0.00\%$	$\color{green}1/1$ $\color{green}+0.00\%$	$\color{green}115/115$ $\color{green}+0.00\%$
math/iter/tools/map	$\color{green}275/275$ $\color{green}+0.00\%$	$\color{green}30/30$ $\color{green}+0.00\%$	$\color{green}5/5$ $\color{green}+0.00\%$	$\color{green}275/275$ $\color{green}+0.00\%$

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