refactor: remove unused generics

[Planeshifter]

Description

What is the purpose of this pull request?

This pull request removes the unused single-use generic type parameter from all six dstdev* signatures (dstdev, dstdevch, dstdevpn, dstdevtk, dstdevwd, dstdevyc), inlining the array element type to match the non-generic convention already used by dvariance, variance, and stdev. The return type is the fixed number, so type-checking behavior is unchanged.

This is part of a series of follow-up PRs addressing findings from a TypeScript declaration audit of the stats namespace (documentation-only fixes landed separately in #12482).

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? 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

This change was surfaced by a Claude Code audit of the stats namespace TypeScript declarations. The fix was verified against the implementation and declaration test before submission, and reviewed by myself.

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/ndarray/dstdev	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$
stats/base/ndarray/dstdevch	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$
stats/base/ndarray/dstdevpn	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$
stats/base/ndarray/dstdevtk	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$
stats/base/ndarray/dstdevwd	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$
stats/base/ndarray/dstdevyc	$\color{green}123/123$ $\color{green}+100.00\%$	$\color{green}3/3$ $\color{green}+100.00\%$	$\color{green}1/1$ $\color{green}+100.00\%$	$\color{green}123/123$ $\color{green}+100.00\%$

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