feat: add support for float16 data type

[stdlib-bot]

This PR updates TypeScript declarations for the @stdlib/ndarray namespace.

Reviewer Checklist

• Check the scope of the changes (following Conventional Commits):
  • Are these new APIs? Then this is a feat.
  • Are these changes to existing APIs that could break compatibility? Then this is a feat! (i.e., a breaking change).
  • Are these only documentation changes to existing APIs? Then this is docs.
• Update the PR title to align with the change type (feat, feat!, or docs).
• Approve the PR once you are confident about the classification and changes made.

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
ndarray	$\\color{red}211935/393887$ $\\color{green}+53.81\\%$	$\\color{red}2443/2490$ $\\color{green}+98.11\\%$	$\\color{red}51/2051$ $\\color{green}+2.49\\%$	$\\color{red}211935/393887$ $\\color{green}+53.81\\%$

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