feat: update assert TypeScript declarations

[stdlib-bot]

This PR updates TypeScript declarations for the @stdlib/assert 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
assert	$\color{red}45336/48802$ $\color{green}+92.90%$	$\color{red}874/992$ $\color{green}+88.10%$	$\color{red}61/421$ $\color{green}+14.49%$	$\color{red}45336/48802$ $\color{green}+92.90%$

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

[kgryte]

As the CI failure is not due to changes introduced in this PR, I'll go ahead and merge.