feat: update complex/base TypeScript declarations

[stdlib-bot]

This PR updates TypeScript declarations for the @stdlib/complex/base 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
complex/base	$\color{red}680/1101$ $\color{green}+61.76%$	$\color{green}12/12$ $\color{green}+100.00%$	$\color{red}0/5$ $\color{green}+0.00%$	$\color{red}680/1101$ $\color{green}+61.76%$

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